Makes it clearer which files are actually used in libcheck and which are used
for cross-platform compatibility. This is going to be especially useful when we
add all the libcompat fallback code that upstream libcheck has which will add
about 6 new files.
https://bugzilla.gnome.org/show_bug.cgi?id=775870
Hurd also defines __MACH__, but it does not have mach_absolute_time. Use
the more strict __APPLE__ instead.
Has also been sent upstream: https://github.com/libcheck/check/pull/65
This lifts the files almost verbatim (the changes being running though
gst-indent and fixing the FSF address) from the upstream respository.
Therefore this commit reverts some GStreamer-specific patches to check
that will be reintroduced next.
Fixes https://bugzilla.gnome.org/show_bug.cgi?id=727826