Merge branch 'fix_parallel_build' into 'master'

Merge branch 'fix_parallel_build' into 'master'

build-sys: use proper dependencies on libproc.la

Use `LDADD` or `*_LDADD` instead of `AM_LDFLAGS` to refer to `libproc.la`.

This is recommended in the automake manual:
http://www.gnu.org/software/automake/manual/html_node/Linking.html

Before this commit, parallel builds may break, as there is no explicit dependency to ensure the library is built before the binaries that try to link to it.

Tested by running `make -jNN` repeatedly for different levels of parallelism to ensure the build works. Also checked that `make check` and `make distcheck` still work as expected. Also made sure that a parallel make invocation works with `make -j distcheck`.

Reported-by: Jim Warner <james.warner@comcast.net>
Signed-off-by: Filipe Brandenburger <filbranden@google.com>
See merge request !2