Emacs ports: Build using GCC when NATIVECOMP is on

In order to allow concurrent installation, the GCC ports, as of 0338e04,
moved some header files to internal locations. Emacs built with
NATIVECOMP requires GCC jit libraries. Rather than patching Emacs to
search in those internal locations, build Emacs with GCC when NATIVECOMP
is turned on.

PR: 257060
Tested by: jcfyecrayz@liamekaens.com, yasu
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D37275