bsd.sys.mk and bsd.own.mk
- Add protection requiring that:
1. bsd.sys.mk is not include from other Makefiles directly
2. bsd.own.mk must be included before bsd.sys.mk since it
sets variables that bsd.sys.mk uses as conditionals.
This is step 1 of removing all variable settings from bsd.sys.mk and
leaving behind only rules. This way, the structure of a standard Makefile
is:
variable overrides
optionally include bsd.own.mk
optionally include bsd.endian.mk
variable settings that use variables defined in bsd.own.mk
include a one or more rule .mk files (such as bsd.prog.mk etc)
