Remove $FreeBSD$: one-line .h pattern

Remove /^\s*\*+\s*\$FreeBSD\$.*$\n/

libregex: Add a symbol map

kib points out that trying to re-use symbol versioning from libc is dirty
and wrong. The implementation in libregex is incompatible by design with the
implementation in libc. Using the symbol versions from libc can and likely
will cause confusions for linkers and bring unexpected behavior for
consumers that unwillingly (transitively) link against libregex.

Reported by: kib