• Use addprefix instead of manually concatenating $(srcdir)
• Use AM_V_GEN instead of QUIET_GEN, to avoid inter-dependencies
• Do basic checks on GLIB_MKENUMS and GLIB_GENMARSHAL being defined
• Do checks on the required variables being defined
for the marshal files $(srcdir) was getting prefixed twice since my last
commit (2cc88f1140) since it was already being prefixed including
Makefile.am. The problem with prefixing it in the includer file though is
that the Make variable substitutions like :.list=.h mean we end up
generating into the $(srcdir). This removes the prefix added in
clutter/Makefile.am
We were also missing a $(srcdir) prefix when setting EXTRA_DIST
Out of tree builds were broken in commit 46b736f42e since we didn't
explicitly use $(srcdir) to find the input files for glib-mkenums and
glib-genmarshal.
The rules to create signal marshallers and enumeration GTypes are
usually copied and pasted all over different projects, though they
are pretty generic and, given a little bit of parametrization, can
be put in separate Makefile.am files and included whenever needed.
