crt: Fix condition for fabsf in api-ms-win-crt-math

This was changed erroneously in
95ad23696f57b0f966525b574096bd53d48c773a; fabsf is only available
on arm/aarch64 - it doesn't have anything to do with whether
we are compatible with UCRT regarding long doubles.

Also fix _o_fabsf in ucrtbase-common.def.in which also was changed
erroneously in the same way.

Signed-off-by: Martin Storsjö <martin@martin.st>