Eliminate "const" from extern const to fix breakeage since r135184 on msvc.

MSVC decorates (and distinguishes) "const" in mangler. It brought linkage error between "extern const" declarations and definitions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@135269 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/InstrInfoEmitter.cpp b/utils/TableGen/InstrInfoEmitter.cpp
index d3c2d63..5ebaf17 100644
--- a/utils/TableGen/InstrInfoEmitter.cpp
+++ b/utils/TableGen/InstrInfoEmitter.cpp
@@ -239,7 +239,7 @@
   OS << "#undef GET_INSTRINFO_CTOR\n";
 
   OS << "namespace llvm {\n";
-  OS << "extern const MCInstrDesc " << TargetName << "Insts[];\n";
+  OS << "extern MCInstrDesc " << TargetName << "Insts[];\n";
   OS << ClassName << "::" << ClassName << "(int SO, int DO)\n"
      << "  : TargetInstrInfoImpl(SO, DO) {\n"
      << "  InitMCInstrInfo(" << TargetName << "Insts, "