lang/gcc16: Fix build on arm64

GCC upstream has removed conditional definitions for some constants,
defining them directly with the same values used on Linux. However,
FreeBSD values for the same constants are different. Then revert
upstream commit.

Co-authored-by: Mark Millard <marklmi26-fbsd@yahoo.com>
PR: 294062
Reported by: Luke Yasuda <jing@jing.rocks>