There's a closed pull request on the void-packages repository

gpsim: remove #include "../config.h" from breakpoints.h to prevent errors about missing config.h
https://github.com/void-linux/void-packages/pull/25944

Description:
When using `breakpoints.h` from `gpsim-devel` package, program fails to build due to missing `config.h` header.
AFAIK this header is generated automatically by `autotools` and exists only during the build process.

Another fix is installing `eXdbm` headers along with `gpsim`.