Remove the plug/socket exception, and add exceptions for non-X11
windowing systems.
Additionally, speed up the file generation by avoiding string
concatenation in Python.
When we reconfigure, `configure_file()` is called again, and
`*.gresource.xml` files are regenerated, which causes many (all?)
binaries to be relinked. Now we only write those out if the contents
actually changed (or if the output didn't already exist).
This is exactly what Meson already does with `configure_file()` when
`command:` is not used.
While we're at it, also do the same for `gen-c-array.py` and
`gentypefuncs.py` for completeness. Now even if the input to those
changes, re-building of those custom targets may not result in
relinking if the outputted C files have the same contents.
On Python-3.x, we need to set the encoding when opening files, when this
script is run, as it might contain items that are not supported by the
system's locale (for example, non-English Windows). So, we use a
wrapper to set the encoding on Python 3.x, but open the file as we did
when using Python 2.x, since file encodings are not supported there.
https://bugzilla.gnome.org/show_bug.cgi?id=785210
GSK has various enumeration types that are currently not used; while
they may go away, currently they are built and introspected. If we want
the introspection machinery to work, and still use static libraries to
build GDK and GSK into the GTK shared library, then we need to reference
the get_type() function of these enumeration types somewhere, to avoid
the linker discarding it, and thus breaking the build.
As luck would have it, we have an autogenerated bit of C that refers to
all the get_type() functions in the library; if we add the GSK types to
it, then we get the reference we're looking for, and the build succeeds.
