Before, loading a module would be guarded by an optional platform
condition. This made it possible to avoid loading and evaluating a
module if it did not support the host platform.
Unfortunately, this made it impossible to share a single configuration
between GNU/Linux and Darwin hosts, which some wish to do.
This removes the conditional load and instead inserts host platform
assertions in the modules that are platform specific.
Fixes#1906
Before the profile commands would not run if a single package is
installed since `buildEnv` will produce a symlink directly to that
package. By adding this dummy package we ensure that a real directory
will be generated.
Fixes#1392
This change stops update-mime-database from running unless the
`share/mime/packages` directory is writable. For some reason it
appears to be read-only on WSL1.
Fixes#1192
