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

llvm-svn: 239464
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
index 1ac656d..de0e67a 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
@@ -790,10 +790,8 @@
 
 MCAsmBackend *llvm::createX86_32AsmBackend(const Target &T,
                                            const MCRegisterInfo &MRI,
-                                           StringRef TT,
+                                           const Triple &TheTriple,
                                            StringRef CPU) {
-  Triple TheTriple(TT);
-
   if (TheTriple.isOSBinFormatMachO())
     return new DarwinX86_32AsmBackend(T, MRI, CPU);
 
@@ -806,10 +804,8 @@
 
 MCAsmBackend *llvm::createX86_64AsmBackend(const Target &T,
                                            const MCRegisterInfo &MRI,
-                                           StringRef TT,
+                                           const Triple &TheTriple,
                                            StringRef CPU) {
-  Triple TheTriple(TT);
-
   if (TheTriple.isOSBinFormatMachO()) {
     MachO::CPUSubTypeX86 CS =
         StringSwitch<MachO::CPUSubTypeX86>(TheTriple.getArchName())