Replace string GNU Triples with llvm::Triple in MCAsmBackend subclasses and create*AsmBackend(). NFC.

Summary:
This continues the patch series to eliminate StringRef forms of GNU triples
from the internals of LLVM that began in r239036.

Reviewers: echristo, rafael

Reviewed By: rafael

Subscribers: rafael, llvm-commits, rengolin

Differential Revision: http://reviews.llvm.org/D10243

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239464 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Sparc/MCTargetDesc/SparcAsmBackend.cpp

@@ -297,10 +297,8 @@ namespace {
 
 } // end anonymous namespace
 
-
 MCAsmBackend *llvm::createSparcAsmBackend(const Target &T,
                                           const MCRegisterInfo &MRI,
-                                          StringRef TT,
-                                          StringRef CPU) {
-  return new ELFSparcAsmBackend(T, Triple(TT).getOS());
+                                          const Triple &TT, StringRef CPU) {
+  return new ELFSparcAsmBackend(T, TT.getOS());
 }