TOOL_DEPENDS

[Robert Swindells <rjs%fdy2.co.uk@localhost>]

How is TOOL_DEPENDS supposed to be used?

I would like to use lang/ecl as an alternative build tool for lang/sbcl
as ecl works on NetBSD/aarch64 while clisp doesn't.

Just adding TOOL_DEPENDS+= ecl to the lang/sbcl Makefile doesn't work,
it can't find its internal C header files that have been installed
under /usr/pkg/include.

Adding lang/ecl/buildlink3.mk to the lang/sbcl Makefile gets past this
point but it then can't find the library for devel/libffi.

There are a few other packages that use lang/ecl as their runtime
host, these explicitly include devel/libffi/buildlink3.mk.

Should devel/libffi/buildlink3.mk be in lang/ecl/buildlink3.mk and
lang/sbcl/Makefile include lang/ecl/buildlink3.mk as well as defining
TOOL_DEPENDS?