Pass StringRef by value.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86251 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86TargetMachine.cpp b/lib/Target/X86/X86TargetMachine.cpp
index a61de1c..5d58a87 100644
--- a/lib/Target/X86/X86TargetMachine.cpp
+++ b/lib/Target/X86/X86TargetMachine.cpp
@@ -22,8 +22,7 @@
 #include "llvm/Target/TargetRegistry.h"
 using namespace llvm;
 
-static const MCAsmInfo *createMCAsmInfo(const Target &T,
-                                                const StringRef &TT) {
+static const MCAsmInfo *createMCAsmInfo(const Target &T, StringRef TT) {
   Triple TheTriple(TT);
   switch (TheTriple.getOS()) {
   case Triple::Darwin: