STRERROR_R_CHAR_P broken

After http://git.savannah.gnu.org/cgit/autoconf.git/commit/lib/autoconf/functions.m4?id=326c9a547423d25c621bc5c0ef76edbf6eda8c92
detection fails because <string.h> is no longer included.

checking whether strerror_r is declared... yes
checking whether strerror_r returns char *... no

configure:11444: x86_64-mageia-linux-gnu-gcc -c -O2 -g -pipe -Wformat
-Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector
--param=ssp-buffer-size=4 -fstack-protector-all
-fasynchronous-unwind-tables -I/usr/include/et -fPIC
-fno-strict-aliasing -fstack-protector-all -I/usr/include/et
conftest.c >&5
conftest.c: In function 'main':
conftest.c:77:14: warning: implicit declaration of function
'strerror_r' [-Wimplicit-function-declaration]
   77 |    char x = *strerror_r (0, buf, sizeof buf);
      |              ^~~~~~~~~~
conftest.c:77:13: error: invalid type argument of unary '*' (have 'int')
   77 |    char x = *strerror_r (0, buf, sizeof buf);
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
conftest.c:78:14: warning: initialization of 'char *' from 'int' makes
pointer from integer without a cast [-Wint-conversion]
   78 |    char *p = strerror_r (0, buf, sizeof buf);
      |              ^~~~~~~~~~
configure:11444: $? = 1


The suspicious part of the commit is:

-AC_COMPILE_IFELSE([AC_LANG_PROGRAM([AC_INCLUDES_DEFAULT],
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([],