build: use library rather than cross-directory compilation

build: use library rather than cross-directory compilation

If we use subdir-objects with automake, any reference to a
cross-directory .c file will result in automake creating
rules that track dependency in the cross directory.  But this
presents a problem during 'make distclean' - if the cross
directory is cleaned up first, then the daemon directory will
be left with dangling references to .Po dependency files that
no longer exist.

Meanwhile, referring to the cross-directory .c file means
that we are compiling the file twice - once in src, and once
in daemon.  Better is to compile just once in src into a
convenience library, and then use that library from daemon.

The tests directory had a similar situation of a cross-directory
.c file; to solve that, we actually need a convenience library.

* daemon/Makefile.am (DAEMON_SOURCES): Drop .c files...
(libvirtd_LDADD): ...and instead use library.
(libvirtd_conf_la_SOURCES): Declare a new convenience library.
(libvirtd_LDFLAGS): Drop duplicate flag.
* tests/Makefile.am (libvirtdconftest_SOURCES): Drop .c file...
(libvirtdconftest_LDADD): ..and instead use library.

Signed-off-by: Eric Blake <eblake@redhat.com>