Fix ‘restrict’ on MSVC and on Solaris 11.4 g++

Problem and fix reported by Bruno Haible in:
https://lists.gnu.org/r/bug-gnulib/2026-05/msg00069.html
* lib/autoconf/c.m4 (AC_C_RESTRICT): Ignore the value of
__STDC_VERSION__ on MSVC or in C++ mode.
2 files changed