crt: Move ARM long double symbol aliases to def-include/msvcrt-common.def.in

Deduplicate aliases from msvcrt.def.in and ucrtbase.def.in to
def-include/msvcrt-common.def.in.

Note that powl alias was defined only in ucrtbase.def.in, so do not define
it for non-UCRT builds.

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