[Driver] Add support for -fno-builtin-foo options.

Addresses PR4941 and rdar://6756912.
http://reviews.llvm.org/D15195

llvm-svn: 256937
diff --git a/clang/lib/Basic/LangOptions.cpp b/clang/lib/Basic/LangOptions.cpp
index 2c87845..1b08b06 100644
--- a/clang/lib/Basic/LangOptions.cpp
+++ b/clang/lib/Basic/LangOptions.cpp
@@ -11,6 +11,7 @@
 //
 //===----------------------------------------------------------------------===//
 #include "clang/Basic/LangOptions.h"
+#include "llvm/ADT/StringRef.h"
 
 using namespace clang;
 
@@ -36,3 +37,10 @@
   ImplementationOfModule.clear();
 }
 
+bool LangOptions::isNoBuiltinFunc(const char *Name) const {
+  StringRef FuncName(Name);
+  for (unsigned i = 0, e = NoBuiltinFuncs.size(); i != e; ++i)
+    if (FuncName.equals(NoBuiltinFuncs[i]))
+      return true;
+  return false;
+}