Remove some legacy mingw-w64 gcc struct info

[martell]

Summary

GCC versions starting at 4.8+ conform to standard Windows 64-bit ABI.
Not quite sure if we should keep this to support mingw-w64 and gcc 4.6
Thoughts ?

Also it seems to fix:
https://llvm.org/bugs/show_bug.cgi?id=24408&list_id=75541

Thanks to awson for the tip

[awson]

Btw, It is a terrible bug.

It is hard to imagine how much C++ code it renders broken on 64-bit mingw-w64 clang. For example, any of hashtable-using code doesn't work etc etc.

[rnk]

Rafael, we don't support pre GCC 4.7 mingw right? They switched to thiscall on 32bit, right? I think we can take a break for x64.

[• rafael]

Correct. I we just switched to the 4.7 abi in r197163.

Cheers,
Rafael

[martell]

Ohh wow thats dated Dec 12 2013
I assume this would be suitable for 3.7.x then also.
This was originally introduced by @chapuni in rL126186
No test case seems to be present for this so I think this should be good to commit.
@rnk LGTY ?

[rnk]

Yeah, lgtm.

[chapuni]

Sorry, I supposed someone removed it. It was really buggy in past.

[martell]

From what I can gather it made sense at the time of gcc 4.6 so I don't think anyone is at fault :)

lib/CodeGen/TargetInfo.cpp

     if (RT->getDecl()->hasFlexibleArrayMember())
       return getNaturalAlignIndirect(Ty, /*ByVal=*/false);
 
-    // FIXME: mingw-w64-gcc emits 128-bit struct as i128
-    if (Width == 128 && IsMingw64)
-      return ABIArgInfo::getDirect(
-          llvm::IntegerType::get(getVMContext(), Width));
   }
 
   // vectorcall adds the concept of a homogenous vector aggregate, similar to