[r16-4338 Regression] FAIL: c-c++-common/gomp/append-args-7.c -std=c++26 (test for excess errors) on Linux/x86_64

[Jiang, Haochen]

On Linux/x86_64,

4e44fe4280bf2d9ddc135dec18ec109805c539b9 is the first bad commit
commit 4e44fe4280bf2d9ddc135dec18ec109805c539b9
Author: Jakub Jelinek <ja...@redhat.com>
Date:   Thu Oct 9 22:41:30 2025 +0200

    c++: C++26 va_start - part of P3348R4 - C++26 should refer to C23 not C17

caused

FAIL: c-c++-common/gomp/append-args-7.c  -std=c++26  scan-tree-dump-times 
gimple "f3 \\(obj1, obj2, 1, a, cp, d\\);" 1
FAIL: c-c++-common/gomp/append-args-7.c  -std=c++26 (test for excess errors)

with GCC configured with

../../gcc/configure 
--prefix=/export/users3/haochenj/src/gcc-bisect/master/master/r16-4338/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="gomp.exp=c-c++-common/gomp/append-args-7.c 
--target_board='unix{-m32}'"
$ cd {build_dir}/gcc && make check 
RUNTESTFLAGS="gomp.exp=c-c++-common/gomp/append-args-7.c 
--target_board='unix{-m32\ -march=cascadelake}'"
$ cd {build_dir}/gcc && make check 
RUNTESTFLAGS="gomp.exp=c-c++-common/gomp/append-args-7.c 
--target_board='unix{-m64}'"
$ cd {build_dir}/gcc && make check 
RUNTESTFLAGS="gomp.exp=c-c++-common/gomp/append-args-7.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.)