MC: Add partial x86-64 support to COFF.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111728 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86MCAsmInfo.cpp b/lib/Target/X86/X86MCAsmInfo.cpp
index 2b8720b..36badb4 100644
--- a/lib/Target/X86/X86MCAsmInfo.cpp
+++ b/lib/Target/X86/X86MCAsmInfo.cpp
@@ -103,6 +103,9 @@
 }
 
 X86MCAsmInfoCOFF::X86MCAsmInfoCOFF(const Triple &Triple) {
+  if (Triple.getArch() == Triple::x86_64)
+    GlobalPrefix = "";
+
   AsmTransCBE = x86_asm_table;
   AssemblerDialect = AsmWriterFlavor;