By default, pkg-config output will not include Requires.private
dependencies (which specify dependencies that only apply when building
statically). It will only do this when passed --static. In
pkgsStatic, let's ensure pkg-config is always operating in static
mode, because pkgsStatic will ensure that any libraries pkg-config
might find will always be static, and so will always need their
Requires.private dependencies.
This is very useful for Meson builds, because otherwise Meson will
only pass --static to pkg-config if the dependency was explicitly
"static : true", which is not likely to be the case for most stuff
we're building.
An alternative proposal was to patch Meson to add a special
environment variable to force dependencies to be "static : true". I
feel that the approach I've taken here is less invasive.
This is much better because then we can freely keep the comments up to
date without causing mass rebuilds.
Someday, somebody should make the same change with `cc-wrapper` and
`bintools-wrapper`.
