Blackfin arch: revise anomaly handling by basing things on the compiler not the kconfig defines

revise anomaly handling by basing things on the compiler not the kconfig defines,
so the header is stable and usable outside of the kernel. This also allows us to
move some code from preprocessing to compiling (gcc culls dead code)
which should help with code quality (readability, catch minor bugs, etc...).

Signed-off-by: Mike Frysinger <michael.frysinger@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>