5f9c61e08f
gudev/gudev.h is included unconditionally, so only enable the gbm backend if gudev was actually found. This also matches the meson build behaviour. Should fix build on GNOME SDK builder.
All aclocal .m4 files we need are put here and cat'd to acinclude.m4 in the source root. Official ones (taken from the relevant devel packages) are named as-is, unofficial ones (or changed ones) get a gst-prefix.