compile_et macros to generate source and headers separately

Common makefile macros to generate headers and source files
separately using the new compile_et -emit option.

Reviewed-on: http://gerrit.openafs.org/10869
Reviewed-by: D Brashear <shadow@your-file-system.com>
Tested-by: D Brashear <shadow@your-file-system.com>
(cherry picked from commit be36376b244d1d94b24cb8fce44810fb31b7b5ce)

Change-Id: Ic9cf078f6a013e7529ae8f11b0378173e64ee680
Reviewed-on: http://gerrit.openafs.org/11237
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>