[r16-4421 Regression] FAIL: std/ranges/adaptors/93978.cc -std=gnu++26 (test for excess errors) on Linux/x86_64

[Jiang, Haochen]

On Linux/x86_64,

59cabe08b57a262d5d7d041515889a012189c908 is the first bad commit
commit 59cabe08b57a262d5d7d041515889a012189c908
Author: Tomasz KamiÅ"ski <tkaminsk@redhat.com>
Date:   Tue Jul 8 18:50:50 2025 +0200

    libstdc++: Implement _Escaping_sink to avoid construction of string

caused

FAIL: g++.dg/warn/uninit-pr105562.C  -std=gnu++26 (test for excess errors)
FAIL: g++.dg/warn/Wstringop-overflow-6.C  -std=gnu++26 (test for excess errors)
FAIL: g++.old-deja/g++.robertl/eb73.C  -std=gnu++26 (test for excess errors)
FAIL: std/ranges/adaptors/93978.cc  -std=gnu++26 (test for excess errors)

with GCC configured with

../../gcc/configure --prefix=/export/users3/haochenj/src/gcc-bisect/master/master/r16-4421/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="dg.exp=g++.dg/warn/uninit-pr105562.C --target_board='unix{-m32}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=g++.dg/warn/uninit-pr105562.C --target_board='unix{-m32\ -march=cascadelake}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=g++.dg/warn/uninit-pr105562.C --target_board='unix{-m64}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=g++.dg/warn/uninit-pr105562.C --target_board='unix{-m64\ -march=cascadelake}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=g++.dg/warn/Wstringop-overflow-6.C --target_board='unix{-m32}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=g++.dg/warn/Wstringop-overflow-6.C --target_board='unix{-m32\ -march=cascadelake}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=g++.dg/warn/Wstringop-overflow-6.C --target_board='unix{-m64}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=g++.dg/warn/Wstringop-overflow-6.C --target_board='unix{-m64\ -march=cascadelake}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="old-deja.exp=g++.old-deja/g++.robertl/eb73.C --target_board='unix{-m32}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="old-deja.exp=g++.old-deja/g++.robertl/eb73.C --target_board='unix{-m32\ -march=cascadelake}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="old-deja.exp=g++.old-deja/g++.robertl/eb73.C --target_board='unix{-m64}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="old-deja.exp=g++.old-deja/g++.robertl/eb73.C --target_board='unix{-m64\ -march=cascadelake}'"
$ cd {build_dir}/x86_64-linux/libstdc++-v3/testsuite && make check RUNTESTFLAGS="conformance.exp=std/ranges/adaptors/93978.cc --target_board='unix{-m32}'"
$ cd {build_dir}/x86_64-linux/libstdc++-v3/testsuite && make check RUNTESTFLAGS="conformance.exp=std/ranges/adaptors/93978.cc --target_board='unix{-m32\ -march=cascadelake}'"
$ cd {build_dir}/x86_64-linux/libstdc++-v3/testsuite && make check RUNTESTFLAGS="conformance.exp=std/ranges/adaptors/93978.cc --target_board='unix{-m64}'"
$ cd {build_dir}/x86_64-linux/libstdc++-v3/testsuite && make check RUNTESTFLAGS="conformance.exp=std/ranges/adaptors/93978.cc --target_board='unix{-m64\ -march=cascadelake}'"

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