configure.ac: error out if python/mako is not found when required

In case of using a distribution tarball (or a dirty git tree) one can
have the generated sources locally. Make configure.ac error out
otherwise, to alert that about the unmet requirement(s) of python/mako.

v2: Check only for a single file for each dependency.

Suggested-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
1 file changed