[PATCH] CodeGen: Stick constant pool entries in COMDAT sections for WinCOFF

[Jim Grosbach]

Rather terrifying how MSVC does this stuff, but patch LGTM.

Minor nit inline.

================
Comment at: lib/Target/X86/X86TargetObjectFile.cpp:165
@@ +164,3 @@
+                COFF::IMAGE_COMDAT_SELECT_ANY));
+        MCSymbol *Sym = S->getCOMDATSymbol();
+        return S;
----------------
"Sym" is unused.

I think you can just directly do:

```
return getContext().getCOFFSection(".rdata", Characteristics, Kind, COMDATSymName, COFF::IMAGE_COMDAT_SELECT_ANY));
```

http://reviews.llvm.org/D4482