Makefile.include: support make clean all

Historically $(OBJECTDIR) was created when Makefile.include is read.  A
consequence is that combining "clean" with "all" (or any other build
target) results in an error because the clean removes the object
directory that is required to exist when building dependencies.
Creating $(OBJECTDIR) on-demand ensures it is present when needed.

Removed creation of $(OBJECTDIR) on initial read, and added an order-only
dependency forcing its creation all Makefile* rules where the target is
explicitly or implicitly in $(OBJECTDIR).