Add support for thiscall calling convention.
Patch by Charles Davis and Steven Watanabe!

llvm-svn: 103902
diff --git a/llvm/lib/Target/CBackend/CBackend.cpp b/llvm/lib/Target/CBackend/CBackend.cpp
index cc9e1d7..55b8aaa 100644
--- a/llvm/lib/Target/CBackend/CBackend.cpp
+++ b/llvm/lib/Target/CBackend/CBackend.cpp
@@ -2165,6 +2165,9 @@
    case CallingConv::X86_FastCall:
     Out << "__attribute__((fastcall)) ";
     break;
+   case CallingConv::X86_ThisCall:
+    Out << "__attribute__((thiscall)) ";
+    break;
    default:
     break;
   }