Fix libatomic multilib parallel build (PR other/67627)

The all-multi target may be built in parallel with the %_.lo
targets which generate make dependencies that are parsed during
the build of all-multi.

This patch forces all-multi to only run after the *_.lo targets
are done.

libatomic:
	PR other/67627
	* Makefile.am (all-multi): Add dependency.
	* Makefile.in: Regenerate.

From-SVN: r232102