package/apr: fix build failure with GCC >= 14

The workaround in 3d06661fc1 for the
broken C23 check was incorrect: When overriding ac_cv_prog_cc_c23 the
value must either be "no" (to indicate that C23 is not supported) or
contain the command line parameters to enable C23 with the C compiler
in use (e.g. "-std=gnu23", may be an empty string if appropriate). The
workaround set it to "yes" for host GCC >= 14, making builds fail.

However, the original issue was that apr may try to enable C23 in host
CC calls if the target CC supports it. So instead of figuring out the
correct arguments for GCC >= 14, we can set ac_cv_prog_cc_c23=no only
for host GCC <= 13 and leave it unset otherwise, as in that case
enabling C23 will do no harm.

Fixes: 3d06661fc1
Fixes:
- https://autobuild.buildroot.net/results/77c/77cd5456169e04c2f92dc328c4b6828513d1195f/
- https://autobuild.buildroot.net/results/7a4/7a4fb2b21027f98df607871d9fe0dd234d44aebb/
- https://autobuild.buildroot.net/results/a6c/a6cef4c5965fdeb40d3b39cbd40941329f4fc1c8/
(and more)

Tested-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Fiona Klute <fiona.klute@gmx.de>
Signed-off-by: Romain Naour <romain.naour@smile.fr>

package/apr/apr.mk

@@ -34,7 +34,6 @@ APR_CONF_ENV = \
 	ac_cv_mmap__dev_zero=yes \
 	ac_cv_func_setpgrp_void=yes \
 	apr_cv_process_shared_works=yes \
-	ac_cv_prog_cc_c23=$(if $(BR2_HOST_GCC_AT_LEAST_14),yes,no) \
 	apr_cv_mutex_robust_shared=no \
 	apr_cv_tcp_nodelay_with_cork=yes \
 	ac_cv_sizeof_struct_iovec=8 \
@@ -51,6 +50,10 @@ APR_CONF_ENV = \
 	apr_preload_done=yes
 APR_CONFIG_SCRIPTS = apr-1-config
 
+ifeq ($(BR2_HOST_GCC_AT_LEAST_14),)
+APR_CONF_ENV += ac_cv_prog_cc_c23=no
+endif
+
 # Doesn't even try to guess when cross compiling
 ifeq ($(BR2_TOOLCHAIN_HAS_THREADS),y)
 APR_CONF_ENV += apr_cv_pthreads_lib="-lpthread"