[login_manager] Makefile needs to be parallelizable
[login_manager] Makefile needs to be parallelizable

I had a rule wrong that allowed the parallelization of protobuf bindings generation and compilation that depends on those bindings.  Fix it.

BUG=None
TEST=emerge-x86-generic chromeos-login

Change-Id: I5308b4158dc1a28ba560e733544820bae1768a42

R=petkov@chromium.org

Review URL: http://codereview.chromium.org/6776031

joshfire/chromiumos-platform-login_manager,joshfire/chromiumos-platform-login_manager,chadversary/chromiumos.platform.login_manager,chadversary/chromiumos.platform.login_manager,chadversary/chromiumos.platform.login_manager,joshfire/chromiumos-platform-login_manager