Makefiles in this directory are only used during the 'Instance' make
invocation.  The 'Master' invocation (see explanation in
Master/README) decides which tasks are to be done; for each of them,
it calls a recursive make invocation (called an 'Instance' make
invocation), setting GNUSTEP_INSTANCE to the instance name (for
example, 'defaults'), and GNUSTEP_TYPE to the type of instance type
(for example, 'tool').  The make target to build is as in
internal-tool-all.

This means that all makefiles in this directory are executed with a
well defined GNUSTEP_INSTANCE, GNUSTEP_TYPE, and target.

It is safe/required in all these makefiles/makefile fragments to
access the variables needed to build the target for this instance by
using $($(GNUSTEP_INSTANCE)_VARIABLE).  For example, the list of
OBJC_FILES needed to compile the `defaults' instance will have been
defined by the user in the defaults_OBJC_FILES variable.  In this
directory, we access this list using
$($(GNUSTEP_INSTANCE)_OBJC_FILES).

Please note that this makefiles/makefile fragments can't be included
in the Master invocation, they are actually useless in the Master
invocation, because $(GNUSTEP_INSTANCE) is undefined in that case.