[CodeGen] Always use `printReg` to print registers in both MIR and debug
output

As part of the unification of the debug format and the MIR format,
always use `printReg` to print all kinds of registers.

Updated the tests using '_' instead of '%noreg' until we decide which
one we want to be the default one.

Differential Revision: https://reviews.llvm.org/D40421

llvm-svn: 319445
diff --git a/llvm/test/CodeGen/PowerPC/cxx_tlscc64.ll b/llvm/test/CodeGen/PowerPC/cxx_tlscc64.ll
index 0f45652..cfa243f 100644
--- a/llvm/test/CodeGen/PowerPC/cxx_tlscc64.ll
+++ b/llvm/test/CodeGen/PowerPC/cxx_tlscc64.ll
@@ -40,4 +40,4 @@
   ret i32* @sum1
 }
 
-attributes #0 = { nounwind "no-frame-pointer-elim"="true" }
\ No newline at end of file
+attributes #0 = { nounwind "no-frame-pointer-elim"="true" }