Make tail merging the default, except on powerPC.  There was no prior art
for a target-dependent default with a command-line override; this way
should be generally usable.

llvm-svn: 37285
diff --git a/llvm/lib/Target/PowerPC/PPCTargetMachine.h b/llvm/lib/Target/PowerPC/PPCTargetMachine.h
index a249952..fdf9d35 100644
--- a/llvm/lib/Target/PowerPC/PPCTargetMachine.h
+++ b/llvm/lib/Target/PowerPC/PPCTargetMachine.h
@@ -73,6 +73,7 @@
                               MachineCodeEmitter &MCE);
   virtual bool addSimpleCodeEmitter(FunctionPassManager &PM, bool Fast,
                                     MachineCodeEmitter &MCE);
+  virtual const bool DoTailMergeDefault() const;
 };
 
 /// PPC32TargetMachine - PowerPC 32-bit target machine.