CBackend: Fix MSVC build.

This may produce warnings on MSVS, but it's better than failures.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@113834 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/CBackend/CBackend.cpp

@@ -50,6 +50,10 @@
 #include "llvm/System/Host.h"
 #include "llvm/Config/config.h"
 #include <algorithm>
+// Some ms header decided to define setjmp as _setjmp, undo this for this file.
+#ifdef _MSC_VER
+#undef setjmp
+#endif
 using namespace llvm;
 
 extern "C" void LLVMInitializeCBackendTarget() {