Submitted by:
Reviewed by:
More code to parse numeric constants. This checkin includes:
- Feedback from Chris.
- Support for parsing floating point constants.
- Moved the code to "Sema". Changed API in Action.
- More/better error diagnostics.

At this point, the parsing support should be largely complete. Next step
is to work on filling in sensible values (in IntegerLiteral/FloatLiteral).

llvm-svn: 39349