ping: Fixes for guile.m4

[Alex Sassmannshausen]

Hello,

In December Aleix proposed the following patch to address an issue in
guile.m4 whereby guile programs using the autotools infrastructure would
not find guile and other tools on distributions such as Ubuntu:

http://lists.gnu.org/archive/html/guile-devel/2018-12/msg00002.htm

Guile-Hall, which aims to be a newbie friendly way to create new, and
manage existing guile projects, is also affected by this issue.

What's the status at this point?  Is there anything that needs to happen
before this patch can be merged into Guile?

Best wishes,

Alex