[Vala] automake 1.11.1: unable to build vala project out-of-tree

[Andrey Borzenkov <arvidjaar gmail com>]

I'm trying to rebuild systemd
(http://www.freedesktop.org/wiki/Software/systemd) from GIT. It is
using several programs built using vala; in-tree build is OK,
out-of-tree build fails:

{pts/0}% LC_ALL=C make
make  all-am
make[1]: Entering directory `/home/bor/build/systemd'
make[1]: *** No rule to make target
`/home/bor/src/systemd/systemadm_vala.stamp', needed by
`/home/bor/src/systemd/src/systemadm.c'.  Stop.
make[1]: Leaving directory `/home/bor/build/systemd'
make: *** [all] Error 2

Looking at Makefile.in, generated by automake, I cannot understand how
it is supposed to work:

$(srcdir)/src/systemadm.c: $(srcdir)/systemadm_vala.stamp
        @if test -f $@; then :; else \
          rm -f $(srcdir)/systemadm_vala.stamp; \
          $(am__cd) $(srcdir) && $(MAKE) $(AM_MAKEFLAGS) systemadm_vala.stamp; \
        fi
systemadm_vala.stamp: $(systemadm_SOURCES)
        $(AM_V_VALAC)$(VALAC) $(systemadm_VALAFLAGS) $(VALAFLAGS) -C
$(systemadm_SOURCES)
        $(AM_V_at)touch $@

In out-of-tree build $(srcdir)/systemadm_vala.stamp is not the same as
systemadm_vala.stamp, nor can it be. VPATH search does not apply here,
because path does not yet exist; so when it is rebuilt, file name is
used verbatim.

The rules are auto-generated by automake; do I miss something obvious
or out-of -tree build is really not supported?

Thank you!

-andrey