autogen: Update to 5.18.1.

This is a major update to the latest stable version.

Fixes the issue with wrong search path for guile modules.
guile: Drop compat package.

This reverts commit f94d8b9d1d0c064de15820aa3d556ef57b3519fe.

From now we will ship the compat libraries on an own package.
compat-guile: New package.

This is a compat package for the guile 1.8 version.
Merge remote-tracking branch 'stevee/autogen-update'