This patch is related to the following issue:

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=68036

Tried to send it there without success, maybe because of email change.

Found two issues - unspecified version in pkgconfig of gerbv and some
incompatibility with optional geos library.

Related discussions:

- https://github.com/gerbv/gerbv/issues/130
- https://github.com/pcb2gcode/pcb2gcode/issues/626

The attached patch fixes those problems and allows to build pcb2gcode.