Add new explanation for some shortcomings(WPD, CFI) for lexicon

[lizhengxian.123]

Summary

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

[tejohnson]

Thanks for adding these. One suggestion/question below.

llvm/docs/Lexicon.rst

62

I can't find any other examples in this file of where an abbreviation has 2 possible definitions, so there doesn't seem to be any existing convention. I wonder if this case should look like:

**CFI**
Either:
Call Frame Information...

Or:
Control Flow Integrity...

or something similar, to make it clearer that there are 2 definitions being listed. wdyt?

[lizhengxian.123]

Add more notes to tell people that CFI has two meanings.

[tejohnson]

lgtm

[MTC]

llvm/docs/Lexicon.rst

331

Looks like you drop the newline at the end of file.

[lizhengxian.123]

add a newline at the end of file.

llvm/docs/Lexicon.rst

**BURS**
     Bottom Up Rewriting System --- A method of instruction selection for code
     generation.  An example is the `BURG
     <http://www.program-transformation.org/Transform/BURG>`_ tool.
 
 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
     the FDEs.  Each FDE then points to its CIE.
**TBAA**
     Type-Based Alias Analysis
 
 
 W
 -
 
 **WPD**
     Whole Program Devirtualization
 No newline at end of file