configure: Introduce new output variable to ax_check_python_mako_module.m4

This output variables gives more flexibility for future changes
in autoconf to detect if it is needed to auto-generate files and
check for the auto-generation dependencies.

It is still returning error when Python is not installed.

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Reviewed-by: Kai Wasserbäch <kai@dev.carbon-project.org>

m4/ax_check_python_mako_module.m4

@@ -54,8 +54,8 @@ else:
     " | $PYTHON2 -
 
     if test $? -ne 0 ; then
-       AC_MSG_ERROR(mako $1 or later is required.)
+       AC_SUBST(acv_mako_found, 'no')
     else
-        AC_MSG_RESULT(yes)
+       AC_SUBST(acv_mako_found, 'yes')
     fi
 ])