port-amd64/60519: netbsd-11 fails to build with -march=native for modern processors (x86)

["netbsd-gnats%supposedly.org@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60519
>Category:       port-amd64
>Synopsis:       netbsd-11 fails to build with -march=native for modern processors (x86)
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    port-amd64-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Jul 30 17:40:00 +0000 2026
>Originator:     William Green
>Release:        netbsd-11
>Organization:
>Environment:
NetBSD aaa.supposedly.org 11.0_RC7 NetBSD 11.0_RC7 (GENERIC) #0: Thu Jul 23 17:23:58 PPT 2026  aaa%aaa.supposedly.org@localhost:/home/aaa/src/netbsd11/obj/sys/arch/amd64/compile/GENERIC amd64
>Description:
`/build.sh build` with -march=native (see more on cpu-type below) fails while building OpenSSH in crypto/external/bsd/openssh/dist/kexmlkem768x25519.c. Building on Linux with -m amd64 -V "CPUFLAGS= -march=skylake" (etc.) also fails.

Trying to manually compile this file with the same options used by build.sh gives this error:

In file included from /home/aaa/src/netbsd11/src/crypto/external/bsd/openssh/dist/kexmlkem768x25519.c:46:                                                                                                    /home/aaa/src/netbsd11/src/crypto/external/bsd/openssh/dist/libcrux_mlkem768_sha3.h: In function 'libcrux_ml_kem_ind_cpa_unpacked_default_8b_1b':                                                            /home/aaa/src/netbsd11/src/crypto/external/bsd/openssh/dist/libcrux_mlkem768_sha3.h:8112:11: error: array subscript '<unnamed-unsigned:256>[0]' is partly outside array bounds of 'uint8_t[2]' {aka 'unsigned char[2]'} [-Werror=array-bounds]                                                                                                                                                                             8112 |   uint8_t uu____1[32U] = {0U};                                                                                                                                            
                                  |           ^~~~~~~ 
cc1: all warnings being treated as errors           

Trying various values for -march showed this occurs on GCC cpu-types that enable AVX (i.e. this error is generated with -march=sandybridge but not -march=nehalem and ditto for bdver1/barcelona).

Compiling with the base system gcc on 11.0_RC7 (i.e. 12.5.0) instead of the build.sh-built tooldir gcc gives the same error. However gcc15 from pkgsrc compiles without error/warning.
>How-To-Repeat:
Build netbsd-11 sources with CPUFLAGS= -march=sandybridge (or any cpu-type that enables AVX).
>Fix:
Unknown