fd.h: fix build when not building with xtrans

Always include <X11/Xfuncproto.h> for the definition of _X_NORETURN, instead of relying on Xtrans.h to include it indirectly for us.

• Fixes: #2 (closed)
• Fixes: commit cc298d1f

Also includes CI changes to test builds both with and without xtrans to help catch issues like this before release next time, and to drop requirement for Signed-off-by tags in commits from our CI config, to match latest Xorg CI defaults.