keymap: remove "flags" field of xkb_private_action

Private actions have no flags - only serialized data.

Signed-off-by: Ran Benita <ran234@gmail.com>
utils: add a STATIC_ASSERT macro

It'd be nicer to use C11's static_assert(), but it's easier to roll our
own C99 version using a trick I saw in xv6.

Signed-off-by: Ran Benita <ran234@gmail.com>
x11/keymap: handle private actions

Previously we treated them as NoAction().

Signed-off-by: Ran Benita <ran234@gmail.com>
test/x11-keyseq: new test

It is like test/stringcomp, only instead of using
xkb_keymap_new_from_string(), it uses xkbcomp to upload the keymap to a
dummy Xvfb X server and then xkb_x11_keymap_new_from_device().

If any of these components are not present or fails, the test is shown
as skipped.

The test is messy, fragile, limited and depends on external tools, but I
will improve on that later -- it's better to have a test.

Signed-off-by: Ran Benita <ran234@gmail.com>