lang/gcc16-devel: Unbreak on aarch64

FreeBSD defines ElfW(x) to translate Linux's convention to FreeBSD's convention.
GCC defines ElfW to convert its convention to FreeBSD's convention. This patch
removes the conversion defined by GCC so that the FreeBSD conversion only is
applied.

Co-authored-by: Mark Millard <marklmi26-fbsd@yahoo.com>

PR: 282797
Reported by: John F. Carr <jfc@mit.edu>
Email Thread: https://lists.freebsd.org/archives/freebsd-toolchain/2025-May/002282.html