[r16-5625 Regression] FAIL: g++.dg/modules/xtreme-header-8.C -std=c++26 (test for excess errors) on Linux/x86_64

[Haochen Jiang]

On Linux/x86_64,

9ed821d107f7a183f75b4b5d25b32d7f34ca60b5 is the first bad commit
commit 9ed821d107f7a183f75b4b5d25b32d7f34ca60b5
Author: Tomasz Kamiński <tkaminsk@redhat.com>
Date:   Thu Nov 13 14:54:11 2025 +0100

    libstdc++: Optimize functor storage for transform views iterators.

caused

FAIL: g++.dg/modules/xtreme-header-8.C module-cmi xstd (gcm.cache/xstd.gcm)
FAIL: g++.dg/modules/xtreme-header-8.C -std=c++26 (test for excess errors)

with GCC configured with

../../gcc/configure --prefix=/export/users3/haochenj/src/gcc-bisect/master/master/r16-5625/usr --enable-clocale=gnu --with-system-zlib --with-demangler-in-ld --with-fpmath=sse --enable-languages=c,c++,fortran --enable-cet --without-isl --enable-libmpx x86_64-linux --disable-bootstrap

To reproduce:

$ cd {build_dir}/gcc && make check RUNTESTFLAGS="modules.exp=g++.dg/modules/xtreme-header-8.C --target_board='unix{-m32}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="modules.exp=g++.dg/modules/xtreme-header-8.C --target_board='unix{-m32\ -march=cascadelake}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="modules.exp=g++.dg/modules/xtreme-header-8.C --target_board='unix{-m64}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="modules.exp=g++.dg/modules/xtreme-header-8.C --target_board='unix{-m64\ -march=cascadelake}'"

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(If you met problems with cascadelake related, disabling AVX512F in command line might save that.)
(However, please make sure that there is no potential problems with AVX512.)