StringRef'ize EmitSourceFileHeader().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150917 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/TableGen/TableGenBackend.cpp b/lib/TableGen/TableGenBackend.cpp
index 328d9a4..09bcc7a 100644
--- a/lib/TableGen/TableGenBackend.cpp
+++ b/lib/TableGen/TableGenBackend.cpp
@@ -17,7 +17,7 @@
 
 void TableGenBackend::anchor() { }
 
-void TableGenBackend::EmitSourceFileHeader(const std::string &Desc,
+void TableGenBackend::EmitSourceFileHeader(StringRef Desc,
                                            raw_ostream &OS) const {
   OS << "//===- TableGen'erated file -------------------------------------*-"
        " C++ -*-===//\n//\n// " << Desc << "\n//\n// Automatically generate"