[Driver] Mark many target-specific driver-only options as TargetSpecific

so that they get an error on other targets. This change uses let statements to
apply `Flags = [TargetSpecific]` to options (mostly -m*) without specifying `Flags`.
Follow-up to D151590.

For some options, e.g. -mdefault-build-attributes (D31813), -mbranch-likely
(D38168), -mfpu=/-mabi= (6890b9b7), a warning
seems desired in at least certain cases. This is not the best practice, but this
change works around them by not applying `Flags = [TargetSpecific]`.

(
For Intel CPU errata -malign-branch= family options, we also drop the unneeded
NotXarchOption flag. This flag reports an error if the option is used with
-Xarch_*. This error reporting does not seem very useful.
)