[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/Frontend/CodeGenOptions.cpp b/clang/lib/Frontend/CodeGenOptions.cpp
index 75ee47f..50bb9f9 100644
--- a/clang/lib/Frontend/CodeGenOptions.cpp
+++ b/clang/lib/Frontend/CodeGenOptions.cpp
@@ -21,4 +21,12 @@
   memcpy(CoverageVersion, "402*", 4);
 }
 
+bool CodeGenOptions::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;
+}
+
 }  // end namespace clang