make check: mark known-to-fail tests with XFAIL_TESTS.

Without this, make check stopped recursing up at the first
subdirectory failure, in our case in tests/javascript/gtypes,
leading to:

* The incorrect impression that the test suite consisted of
  only 12 tests.

* Making it impossible for make distcheck to pass.

* First-time users wasting time figuring out what in their
  environment was responsible for these failures, as one
  usually expects make check to pass.

See
https://www.gnu.org/software/automake/manual/html_node/Scripts_002dbased-Testsuites.html

https://bugzilla.gnome.org/show_bug.cgi?id=771510