.cfi directive register parsing flexibility.

.cfi directive register parsing flexibility.

Parsing a register name/number for .cfi directives can't assume that a
register name starts with a '%' token. Be more flexible and check for a
register number instead. Still unlikely to be perfect, but it allows us
to parse both plain identifiers as register names and integers as register
numbers, which is what we're wanting to support at this point.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132466 91177308-0d34-0410-b5e6-96231b3b80d8