Use llvm::stable_sort

While touching the code, simplify if feasible.

llvm-svn: 358996
diff --git a/llvm/lib/CodeGen/IfConversion.cpp b/llvm/lib/CodeGen/IfConversion.cpp
index f1ab681..b17a253 100644
--- a/llvm/lib/CodeGen/IfConversion.cpp
+++ b/llvm/lib/CodeGen/IfConversion.cpp
@@ -1316,7 +1316,7 @@
     AnalyzeBlock(MBB, Tokens);
 
   // Sort to favor more complex ifcvt scheme.
-  std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
+  llvm::stable_sort(Tokens, IfcvtTokenCmp);
 }
 
 /// Returns true either if ToMBB is the next block after MBB or that all the