Add mode parameter to Lcase()/Ucase(), mode = 1 = ASCII only
Add compile-time evaluation for Lcase/Ucase ASCII-only mode
rtlib: Move old lcase/ucase functions into legacy modules

The old lcase/ucase functions without mode parameter aren't used by
the compiler anymore now, but we should still keep them in
libfb[mt].a for backwards compatibility with FB 0.24.