[Flang] Move markdown files(.MD) from documentation/ to docs/

Summary:
Other LLVM sub-projects use docs/ folder for documentation files.
Follow LLVM project policy.
Modify `documentation/` references in sources to `docs/`.
This patch doesn't modify files to reStructuredText(.rst) file format.

Reviewed By: DavidTruby, sscalpone

Differential Revision: https://reviews.llvm.org/D85884

flang/README.md

@@ -8,30 +8,30 @@ F18 was subsequently accepted into the LLVM project and rechristened as Flang.
 
 ## Getting Started
 
-Read more about flang in the [documentation directory](documentation).
-Start with the [compiler overview](documentation/Overview.md).
+Read more about flang in the [docs directory](docs).
+Start with the [compiler overview](docs/Overview.md).
 
 To better understand Fortran as a language
 and the specific grammar accepted by flang,
-read [Fortran For C Programmers](documentation/FortranForCProgrammers.md)
+read [Fortran For C Programmers](docs/FortranForCProgrammers.md)
 and
-flang's specifications of the [Fortran grammar](documentation/f2018-grammar.txt)
+flang's specifications of the [Fortran grammar](docs/f2018-grammar.txt)
 and
-the [OpenMP grammar](documentation/OpenMP-4.5-grammar.txt).
+the [OpenMP grammar](docs/OpenMP-4.5-grammar.txt).
 
 Treatment of language extensions is covered
-in [this document](documentation/Extensions.md).
+in [this document](docs/Extensions.md).
 
 To understand the compilers handling of intrinsics,
-see the [discussion of intrinsics](documentation/Intrinsics.md).
+see the [discussion of intrinsics](docs/Intrinsics.md).
 
 To understand how a flang program communicates with libraries at runtime,
-see the discussion of [runtime descriptors](documentation/RuntimeDescriptor.md).
+see the discussion of [runtime descriptors](docs/RuntimeDescriptor.md).
 
 If you're interested in contributing to the compiler,
-read the [style guide](documentation/C++style.md)
+read the [style guide](docs/C++style.md)
 and
-also review [how flang uses modern C++ features](documentation/C++17.md).
+also review [how flang uses modern C++ features](docs/C++17.md).
 
 ## Supported C++ compilers
 

flang/docs/ArrayComposition.md

@@ -1,4 +1,4 @@
-<!--===- documentation/ArrayComposition.md 
+<!--===- docs/ArrayComposition.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/C++17.md

@@ -1,4 +1,4 @@
-<!--===- documentation/C++17.md 
+<!--===- docs/C++17.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/C++style.md

@@ -1,4 +1,4 @@
-<!--===- documentation/C++style.md 
+<!--===- docs/C++style.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/Calls.md

@@ -1,4 +1,4 @@
-<!--===- documentation/Calls.md
+<!--===- docs/Calls.md
 
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/Character.md

@@ -1,4 +1,4 @@
-<!--===- documentation/Character.md
+<!--===- docs/Character.md
 
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/ControlFlowGraph.md

@@ -1,4 +1,4 @@
-<!--===- documentation/ControlFlowGraph.md 
+<!--===- docs/ControlFlowGraph.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/Directives.md

@@ -1,4 +1,4 @@
-<!--===- documentation/Directives.md 
+<!--===- docs/Directives.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/Extensions.md

@@ -1,4 +1,4 @@
-<!--===- documentation/Extensions.md 
+<!--===- docs/Extensions.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/FortranForCProgrammers.md

@@ -1,4 +1,4 @@
-<!--===- documentation/FortranForCProgrammers.md
+<!--===- docs/FortranForCProgrammers.md
 
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/FortranIR.md

@@ -1,4 +1,4 @@
-<!--===- documentation/FortranIR.md 
+<!--===- docs/FortranIR.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/IORuntimeInternals.md

@@ -1,4 +1,4 @@
-<!--===- documentation/IORuntimeInternals.md
+<!--===- docs/IORuntimeInternals.md
 
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/ImplementingASemanticCheck.md

@@ -1,4 +1,4 @@
-<!--===- documentation/ImplementingASemanticCheck.md 
+<!--===- docs/ImplementingASemanticCheck.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/Intrinsics.md

@@ -1,4 +1,4 @@
-<!--===- documentation/Intrinsics.md 
+<!--===- docs/Intrinsics.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/LabelResolution.md

@@ -1,4 +1,4 @@
-<!--===- documentation/LabelResolution.md 
+<!--===- docs/LabelResolution.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/ModFiles.md

@@ -1,4 +1,4 @@
-<!--===- documentation/ModFiles.md 
+<!--===- docs/ModFiles.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/OpenMP-4.5-grammar.txt

@@ -1,4 +1,4 @@
-#===-- documentation/OpenMP-4.5-grammar.txt --------------------------------===#
+#===-- docs/OpenMP-4.5-grammar.txt --------------------------------===#
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.

flang/docs/OpenMP-semantics.md

@@ -1,4 +1,4 @@
-<!--===- documentation/OpenMP-semantics.md 
+<!--===- docs/OpenMP-semantics.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/OptionComparison.md

@@ -1,4 +1,4 @@
-<!--===- documentation/OptionComparison.md 
+<!--===- docs/OptionComparison.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/Overview.md

@@ -1,4 +1,4 @@
-<!--===- documentation/Overview.md 
+<!--===- docs/Overview.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/ParserCombinators.md

@@ -1,4 +1,4 @@
-<!--===- documentation/ParserCombinators.md 
+<!--===- docs/ParserCombinators.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/Parsing.md

@@ -1,4 +1,4 @@
-<!--===- documentation/Parsing.md 
+<!--===- docs/Parsing.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/Preprocessing.md

@@ -1,4 +1,4 @@
-<!--===- documentation/Preprocessing.md 
+<!--===- docs/Preprocessing.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/PullRequestChecklist.md

@@ -1,4 +1,4 @@
-<!--===- documentation/PullRequestChecklist.md 
+<!--===- docs/PullRequestChecklist.md 
 
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/RuntimeDescriptor.md

@@ -1,4 +1,4 @@
-<!--===- documentation/RuntimeDescriptor.md 
+<!--===- docs/RuntimeDescriptor.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/Semantics.md

@@ -1,4 +1,4 @@
-<!--===- documentation/Semantics.md 
+<!--===- docs/Semantics.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.

flang/docs/f2018-grammar.txt

@@ -1,4 +1,4 @@
-#===-- documentation/f2018-grammar.txt -------------------------------------===#
+#===-- docs/f2018-grammar.txt -------------------------------------===#
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.

flang/docs/flang-c-style.el

@@ -1,4 +1,4 @@
-;;===-- documentation/flang-c-style.el ------------------------------------===;;
+;;===-- docs/flang-c-style.el ------------------------------------===;;
 ;;
 ;; Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 ;; See https://llvm.org/LICENSE.txt for license information.

flang/lib/Evaluate/intrinsics.cpp

@@ -30,7 +30,7 @@ class FoldingContext;
 
 // This file defines the supported intrinsic procedures and implements
 // their recognition and validation.  It is largely table-driven.  See
-// documentation/intrinsics.md and section 16 of the Fortran 2018 standard
+// docs/intrinsics.md and section 16 of the Fortran 2018 standard
 // for full details on each of the intrinsics.  Be advised, they have
 // complicated details, and the design of these tables has to accommodate
 // that complexity.