Import registry from SVN 25146
Use LDADD instead of LDFLAGS/DEPENDENCIES.

This is a lot shorter to type, and still gets the dependencies to work
(tested with touch src/dispatch_common.c; make check, and touch
src/egl_common.c; make check).
List X11_LIBS after lib{egl,glx}_common.

Fixes linking with --as-needed.
Add missing dependency on libdl.

Everything I'd linked against the library so far already had a libdl
dependency (through libX11, for example), so I hadn't noticed.
Merge branch 'khronos-registry'