constify the TargetMachine argument used in the subtarget and
lowering constructors.

llvm-svn: 218832
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index e0396fd..c884c0c 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -64,7 +64,7 @@
   return new PPC64LinuxTargetObjectFile();
 }
 
-PPCTargetLowering::PPCTargetLowering(PPCTargetMachine &TM)
+PPCTargetLowering::PPCTargetLowering(const PPCTargetMachine &TM)
     : TargetLowering(TM, createTLOF(Triple(TM.getTargetTriple()))),
       Subtarget(*TM.getSubtargetImpl()) {
   setPow2SDivIsCheap();