[libc++] Make libc++ forward-compatible with AppleClang's definition of __builtin_verbose_trap (#99529)
AppleClang as included in the Xcode 16 beta implements
`__builtin_verbose_trap`, but it implements slightly different semantics
from the ones implemented upstream. This patch makes libc++ compatible
with either definition until we drop support for the version of
AppleClang that differs from upstream.