jchampion: r1702948 doesn't quite work as advertised. -Werror is never
added to CFLAGS because when combined with -Wstrict-prototypes,
the AC_LANG_PROGRAM won't compile (it uses a bare main()).
+ ylavic: Maybe to -Werror case could be handled later, for now this series
+ avoids a lot of "warning: ‘aplog_module_index’ defined but not
+ used [-Wunused-const-variable=]" thanks to AP_MAYBE_UNUSED.
*) core: avoid adding multiple subrequest filters when there are nested
subrequests. PR58292