build: separate source and header compile_et rules

Generate source and header files separately to support parallel make
without contortions.

Add a complete list of dependencies for each generated header file
to avoid build errors during parallel make.

Reviewed-on: http://gerrit.openafs.org/10370
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: D Brashear <shadow@your-file-system.com>
(cherry picked from commit c01236beb5a6ad55cd424f0ccc3a836d737f78f3)

Change-Id: Ib0e3c3b8e0a268f7db741243ce78fed9f6c342c7
Reviewed-on: http://gerrit.openafs.org/11242
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>