Disable parallel building as parallel builds fail due to incomplete
depends between autogenerated CoreSlave.h and it's include sites:
```
CC prealloc_surface_pool_bridge.lo
prealloc_surface_pool_bridge.c:41:10:
fatal error: core/CoreSlave.h: No such file or directory
```
Dependencies are specified manually in src/core/Makefile.am. Instead
of fixing them one by one locally let's disable parallel builds until
upstream fixes them.
continuation of #109595
pkgconfig was aliased in 2018, however, it remained in
all-packages.nix due to its wide usage. This cleans
up the remaining references to pkgs.pkgsconfig and
moves the entry to aliases.nix.
python3Packages.pkgconfig remained unchanged because
it's the canonical name of the upstream package
on pypi.
This seems to have been confusing people, using both xlibs and xorg, etc.
- Avoided renaming local (and different) xlibs binding in gcc*.
- Fixed cases where both xorg and xlibs were used.
Hopefully everything still works as before.
There is a 1.7.x release out but to minimize chances of breaking
dependees I'm only bumping the minimal needed to be compatible with
ilixi (a gui toolkit for directfb that I'm packaging).
