Makefile.inc1: Enable requesting the universe toolchain.

[jhb]

Summary

make universe builds a cross toolchain uner HOST_OBJTMP/tmp via the
universe-toolchain target. However, doing a plain 'make buildworld'
after a universe/tinderbox run (e.g. to reproduce a failure and test
the fix for it), will try to build a new cross toolchain under
OBJTMP/tmp which can be tedious. This commit adds a make variable
(UNIVERSE_TOOLCHAIN) which can be used similar to CROSS_TOOLCHAIN to
request an external toolchain. If this variable is set (value doesn't
matter), the the universe toolchain is used as an external toolchain.

[jhb]

Fix it to work with sub-stages of buildworld.

[jhb]

Makefile.inc1

77

For some reason HOST_OBJTOP isn't the right value here, I end up with /usr/obj/usr/home/john/work/freebsd/main/amd64.amd64/tmp/obj-tools/freebsd13-amd64 instead of /usr/obj/usr/home/john/work/freebsd/main/freebsd13-amd64. I can't figure out exactly how HOST_OBJTOP is set. Hmm, I guess it's just that I need OBJROOT to be different in this case and manually use the different OBJROOT + HOST__TARGET.

This appears to be because different stages in the build use custom OBJROOTs. I have changes to explicitly pass in UNIVERSE_TOOLCHAIN_PATH to those which "fixes" it.

82

This is a debugging hack I can axe. I had hoped that this would avoid the need to not explicitly pass the variable in the various FOOARGS variables, but it did not. :(

[jhb]

Ping?

[imp]

Looks good to me...