automake: add missing git-version.h dependency

compositor/main.c depends on the header, while the dependency isn't
specified. Thus depending on the order of how things are build we could
get a build failure.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>

Makefile.am

@@ -160,6 +160,7 @@ weston_SOURCES = 					\
 # add BUILT_SOURCES to CLEANFILES, but we want to keep git-version.h
 # in case we're building from tarballs.
 
+compositor/main.c : $(top_builddir)/libweston/git-version.h
 libweston/compositor.c : $(top_builddir)/libweston/git-version.h
 
 noinst_LTLIBRARIES +=				\