[riscv] Add some minimal tracing output to InsertVSETVLI

Only available with -debug.  Main purpose is simplifying an upcoming change, and providing tools for debugging problems.

llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp

@@ -1015,6 +1015,8 @@ void RISCVInsertVSETVLI::computeIncomingVLVTYPE(const MachineBasicBlock &MBB) {
     return;
 
   BBInfo.Exit = TmpStatus;
+  LLVM_DEBUG(dbgs() << "Exit state of " << printMBBReference(MBB)
+                    << " changed to " << BBInfo.Exit << "\n");
 
   // Add the successors to the work list so we can propagate the changed exit
   // status.
@@ -1201,6 +1203,8 @@ bool RISCVInsertVSETVLI::runOnMachineFunction(MachineFunction &MF) {
   if (!ST.hasVInstructions())
     return false;
 
+  LLVM_DEBUG(dbgs() << "Entering InsertVSETVLI for " << MF.getName() << "\n");
+
   TII = ST.getInstrInfo();
   MRI = &MF.getRegInfo();