Regressions on master at commit r15-3433 vs commit r15-3431 on Linux/x86_64

[Haochen Jiang]

Regressions on master at commit r15-3433 vs commit r15-3431 on Linux/x86_64
New failures:

New passes:
FAIL: c-c++-common/musttail12.c  -std=c++11 (test for excess errors)
FAIL: c-c++-common/musttail12.c  -std=c++17 (test for excess errors)
FAIL: c-c++-common/musttail12.c  -std=c++26 (test for excess errors)
FAIL: g++.dg/musttail6.C   (test for excess errors)