cpu: micro-optimise feature dumping

the feature-specific macros each make a call to `vlc_CPU()` which involves
making an atomic read of a global variable, then ANDing the return with a
specific feature flag and comparing with zero. rather than do that over and
over pointlessly, just get the flag set once with a direct call to
`vlc_CPU()` and then directly compare with the individual feature flags.

since we've removed the build-time conditional definition of the feature
test macros which defined them as just returning `1` if matching a build
target, this produces no difference in results, whereas if we had not
removed that, the results would not have corresponded with build-time
force-enabled features.