Use const qualifiers with TargetLowering. This eliminates several

const_casts, and it reinforces the design of the Target classes being
immutable.

SelectionDAGISel::IsLegalToFold is now a static member function, because
PIC16 uses it in an unconventional way. There is more room for API
cleanup here.

And PIC16's AsmPrinter no longer uses TargetLowering.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@101635 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/SystemZ/SystemZTargetMachine.h

@@ -49,8 +49,8 @@ public:
     return &InstrInfo.getRegisterInfo();
   }
 
-  virtual SystemZTargetLowering *getTargetLowering() const {
-    return const_cast<SystemZTargetLowering*>(&TLInfo);
+  virtual const SystemZTargetLowering *getTargetLowering() const {
+    return &TLInfo;
   }
 
   virtual bool addInstSelector(PassManagerBase &PM, CodeGenOpt::Level OptLevel);