The pkg-config variables have been added in GLib 2.62.0. Let's fallback
to default names for these tools in such case (`pkg-config` still
returns a 0 return value, but with empty output for absent variables).
Some distributions are renaming Glib/GIO utilities for multi-arch
reasons so pkg-config variables have been added to find the correct name
of a tool. GTK+ should use these variables instead of searching in PATH.
See glib#1796.
While *some* systems alias python to python3 nowdays, this is
not true for eveything. Especially systems that can potentially
offer both python2 and python3.
According to both PEP 394 and PEP 441 its recommended to always
add the 3 in the shebang.
The existing post-install shell script will most likely not work on
Visual Studio builds as there is normally no shell interpreter installed
on the system where the build is done, but the build is normally done in
a standard Windows cmd.exe console.
Instead, use a Python script so that it will work on the platforms that
Python supports.
