[AArch64] Extend CallingConv::X86_64_Win64 to AArch64 as well

Rename the enum value from X86_64_Win64 to plain Win64.

The symbol exposed in the textual IR is changed from 'x86_64_win64cc'
to 'win64cc', but the numeric value is kept, keeping support for
old bitcode.

Differential Revision: https://reviews.llvm.org/D34474

llvm-svn: 308208
diff --git a/llvm/lib/Target/X86/X86FastISel.cpp b/llvm/lib/Target/X86/X86FastISel.cpp
index ee9e781..527e5d5 100644
--- a/llvm/lib/Target/X86/X86FastISel.cpp
+++ b/llvm/lib/Target/X86/X86FastISel.cpp
@@ -1187,7 +1187,7 @@
       CC != CallingConv::X86_StdCall &&
       CC != CallingConv::X86_ThisCall &&
       CC != CallingConv::X86_64_SysV &&
-      CC != CallingConv::X86_64_Win64)
+      CC != CallingConv::Win64)
     return false;
 
   // Don't handle popping bytes if they don't fit the ret's immediate.
@@ -3171,7 +3171,7 @@
   case CallingConv::X86_FastCall:
   case CallingConv::X86_StdCall:
   case CallingConv::X86_ThisCall:
-  case CallingConv::X86_64_Win64:
+  case CallingConv::Win64:
   case CallingConv::X86_64_SysV:
     break;
   }