[docs][Lexicon] Add new explanation for some shortcomings(WPD, CFI) for lexicon

Add explanations for WPD(whole program devirtualization) and another meaning for CFI(control flow Integrity).

Reviewed By: tejohnson

Differential Revision: https://reviews.llvm.org/D122473

llvm/docs/Lexicon.rst

@@ -54,9 +54,16 @@ C
 -
 
 **CFI**
+    This abbreviation has two meanings.
+    Either:
     Call Frame Information. Used in DWARF debug info and in C++ unwind info
     to show how the function prolog lays out the stack frame.
 
+    Or:
+    Control Flow Integrity. A general term for computer security techniques
+    that prevent a wide variety of malware attacks from redirecting the flow
+    of execution (the control flow) of a program.
+
 **CIE**
     Common Information Entry.  A kind of CFI used to reduce the size of FDEs.
     The compiler creates a CIE which contains the information common across all
@@ -152,6 +159,12 @@ I
     if a valid C++ source program were to trigger an assert in Clang when
     compiled, that could be referred to as an "ICE".
 
+**ICF**
+    Identical Code Folding
+
+**ICP**
+    Indirect Call Promotion
+
 **IPA**
     Inter-Procedural Analysis. Refers to any variety of code analysis that
     occurs between procedures, functions or compilation units (modules).
@@ -309,3 +322,10 @@ T
 **TBAA**
     Type-Based Alias Analysis
 
+
+W
+-
+
+**WPD**
+    Whole Program Devirtualization
+