TargetMachine: Indicate whether machine verifier passes.

This adds a callback to the LLVMTargetMachine that lets target indicate
that they do not pass the machine verifier checks in all cases yet.

This is intended to be a temporary measure while the targets are fixed
allowing us to enable the machine verifier by default with
EXPENSIVE_CHECKS enabled!

Differential Revision: https://reviews.llvm.org/D33696

llvm-svn: 304320
diff --git a/llvm/lib/Target/Sparc/SparcTargetMachine.h b/llvm/lib/Target/Sparc/SparcTargetMachine.h
index 48193fe..faf714c 100644
--- a/llvm/lib/Target/Sparc/SparcTargetMachine.h
+++ b/llvm/lib/Target/Sparc/SparcTargetMachine.h
@@ -40,6 +40,10 @@
   TargetLoweringObjectFile *getObjFileLowering() const override {
     return TLOF.get();
   }
+
+  bool isMachineVerifierClean() const override {
+    return false;
+  }
 };
 
 /// Sparc 32-bit target machine