Restore gnu90 for PHP <8.2

Author: NoiseByNorthwest

config.m4

@@ -26,7 +26,8 @@ if test "$PHP_SPX" = "yes"; then
         CFLAGS="$CFLAGS -std=c11"
         AC_MSG_NOTICE([Adding -std=c11 because PHP >= 8.2])
     else
-        AC_MSG_NOTICE([Not adding -std=c11 because PHP < 8.2])
+        CFLAGS="$CFLAGS -std=gnu90"
+        AC_MSG_NOTICE([Adding -std=gnu90 because PHP < 8.2])
     fi
 
     # Disabling typedef-redefinition is required for: