Zabbix

....I..... [ZBX-22307] restored dbschema building on OpenBSD

Due to some naive constructs in Makefile templates, building dbschemas
(or anything else, really) was broken on OpenBSD, as the generated
Makefile fragments were not valid and not accepted by OpenBSD's make,
resulting in compleat breakage of building from source.

These changes fix that by restructuring the database snippet directories
and reworking the generating of some of the patches.