pkg/60121: gcc12: Build fails on modern ARM64 macOS with error ‘_Float16’ does not name a type

["opensauce04%gmail.com@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60121
>Category:       pkg
>Synopsis:       gcc12: Build fails on modern ARM64 macOS with error ?_Float16? does not name a type
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Mar 23 23:35:00 +0000 2026
>Originator:     Daniel
>Release:        2025Q4
>Organization:
>Environment:
Darwin danmbp 25.4.0 Darwin Kernel Version 25.4.0: Thu Mar  5 22:05:44 PST 2026; root:xnu-12377.101.14~18/RELEASE_ARM64_T8142 arm64
>Description:
GCC 12 fails to compile on macOS with the error described above. This is very problematic as GCC 12 is required whenever any package in any dependency tree requires GCC in spite of any attempt to increase the minimum, presumably due to bootstrapping or something else, meaning that a non-insignificant portion of the ports available in pkgsrc will fail to build on affected macOS versions due to some dependency interacting with GCC.

I am experiencing this issue on macOS 26, however I also found a GitHub issue describing the issue occurring on macOS 15. The repository this issue was filed under was a fork of GCC 12 which seems to have managed to address the issue in its most recent commit. The aforementioned issue can be found here: https://github.com/iains/gcc-12-branch/issues/24

Notably, according to the above issue, the problem *only* seems to affect ARM64 Mac devices, with Intel Macs being seemingly unaffected.
>How-To-Repeat:
Attempt to build gcc12 from pkgsrc on either macOS 26 or 15 with an up-to-date Xcode install (Xcode 16 or 26).
>Fix:
This commit as a patch may or may not address the issue?
https://github.com/iains/gcc-12-branch/commit/99533d94172ed7a24c0e54c4ea97e6ae2260409e