Prepare for templated functions.

Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

Only _WIN32 is defined by the compiler, and WIN32 is not standardized
and may be missing.

Closes #169

Allows building without GLib.  This fails to compile currently,
because GLib is still used in the MPD core.

Avoid GLib.

Fixes building with gcc-4.8
Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>

Skip the global destructors.  We don't need them here - we bail out as
quickly as we can.

Prepare to migrate away from GLib.  Currently, we're still using GLib
as a backend.

Migrate the remaining callers to FatalError().

Replaces GLib's GError.