Follow up to r1812263.

As suggested by Joe, add --maintainer/debugger-mode's CFLAGS in
NOTEST_CFLAGS to avoid interractions with autoconf's AC_LANG_PROGRAM.

APACHE_ADD_GCC_CFLAG now also forces -Wno-strict-prototypes for -Werror
to work despite AC_LANG_PROGRAM generating this warning by itself.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1812301 13f79535-47bb-0310-9956-ffa450edef68