* sysdeps/mach/Makefile (mach-before-compile rule): Pass generating=t,
use target mach-before-compile instead of generated.
(mach-before-compile): New target.
* Makerules: Disable use of tls.make if $(generating) is set.
* mach/Makefile: Include mach-syscalls.mk even if no_deps=t.
* sysdeps/mach/hurd/Makefile: Make generated hurd headers depend on
mach-shortcuts.h so mach/ generation happens before hurd/.