[flang] add preliminary README file

Original-commit: flang-compiler/f18@1fc60916fb
Reviewed-on: https://github.com/flang-compiler/f18/pull/6
Tree-same-pre-rewrite: false

flang/README.md

@@ -1 +1,63 @@
 # f18
+
+## Installation of LLVM 5.0    
+    
+    ############ Extract LLVM, CLANG and other from git in current directory. 
+    ############         
+    ############ Remark: 
+    ############    Do we need the Clang sources for F18? 
+    ############    Probably not but its nice to have the Clang source as 
+    ############    example during development.
+    ############
+    ############        
+    
+    ROOT=$(pwd)
+    REL=release_50
+    
+    git clone https://git.llvm.org/git/llvm.git/
+    cd llvm/
+    git checkout $REL
+    
+    cd $ROOT/llvm/tools
+    git clone https://git.llvm.org/git/clang.git/
+    git checkout $REL
+    
+    cd $ROOT/llvm/projects
+    git clone https://git.llvm.org/git/openmp.git/ 
+    cd openmp
+    git checkout $REL
+    
+    cd $ROOT/llvm/projects
+    git clone https://git.llvm.org/git/libcxx.git/
+    cd libcxx
+    git checkout $REL
+    
+    cd $ROOT/llvm/projects
+    git clone https://git.llvm.org/git/libcxxabi.git/
+    cd libcxxabi
+    git checkout $REL
+    
+    # List the version of all git sub-directories 
+    # They should all match $REL
+    for dir in $(find "$ROOT" -name .git) ; do 
+      cd $dir/.. ; 
+      printf " %-15s %s\n" "$(git rev-parse --abbrev-ref HEAD)" "$(pwd)" ; 
+    done
+    
+    
+    ###########  Build LLVM & CLANG in $PREFIX 
+        
+    PREFIX=$ROOT/usr
+    mkdir $PREFIX
+    
+    mkdir $ROOT/llvm/build
+    cd  $ROOT/llvm/build 
+    cmake CMAKE_INSTALL_PREFIX=$PREFIX 
+    make -j 4
+    make install
+    
+## 
+    ######### Add $PREFIX/bin to PATH 
+    
+    
+