Absolute symlinks break when the source is moved to another location. In
the best case, the symlink will be replaced with a copy, but that creates
code duplication. A user who got the packaged source may decide to change
one config.c without realizing that another config.c will get the same
changes.
Don't ignore config.c, it's a regular source file now, albeit very
short.
Testing done: compiled inside and outside build directory.
309fca35ac