Work around maintainer-mode build failure (using autoconf 2.69)

(possibly fallout from r1887279 / pull apache#25 ??)

configure.in

@@ -366,16 +366,16 @@ AC_ARG_ENABLE(debug,[  --enable-debug          Turn on debugging and compile tim
 ])dnl
 
 AC_ARG_ENABLE(maintainer-mode,[  --enable-maintainer-mode  Turn on debugging and compile time warnings],
-  [APR_ADDTO(CFLAGS,-g)
+  [APR_ADDTO(NOTEST_CFLAGS,-g)
    if test "$GCC" = "yes"; then
-     APR_ADDTO(CFLAGS,[-Wall -Wmissing-prototypes -Wstrict-prototypes -Wmissing-declarations])
+     APR_ADDTO(NOTEST_CFLAGS,[-Wall -Wmissing-prototypes -Wstrict-prototypes -Wmissing-declarations])
       case `($CC --version) 2>/dev/null` in
         *clang-900* | *"clang version 5.0.0"*)
-          APR_ADDTO(CFLAGS,[-Wno-error=strict-prototypes])
+          APR_ADDTO(NOTEST_CFLAGS,[-Wno-error=strict-prototypes])
           ;;
       esac
    elif test "$AIX_XLC" = "yes"; then
-     APR_ADDTO(CFLAGS,-qfullpath -qinitauto=FE -qcheck=all -qinfo=pro)
+     APR_ADDTO(NOTEST_CFLAGS,-qfullpath -qinitauto=FE -qcheck=all -qinfo=pro)
    fi
 ])dnl