from MCAsmLexer.h in preparation of supporting other targets. Changed the
X86AsmParser code to reflect this by removing AsmLexer::LexPercent and looking
for AsmToken::Percent when parsing in places that used AsmToken::Register.
Then changed X86ATTAsmParser::ParseRegister to parse out registers as an
AsmToken::Percent followed by an AsmToken::Identifier.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80929 91177308-0d34-0410-b5e6-96231b3b80d8
