This patch adds a flag in MCAsmInfo that indicates whether dwarf register

This patch adds a flag in MCAsmInfo that indicates whether dwarf register
numbers should be printed instead of symbolic register names in
MCAsmStreamer::EmitRegisterName. This is necessary because some versions of
GNU assembler won't accept code in which symbolic register names are used in
cfi directives. There is no change in behavior unless the flag is explicitly
set to true by a backend.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134635 91177308-0d34-0410-b5e6-96231b3b80d8