K 10
svn:author
V 6
brooks
K 8
svn:date
V 27
2020-11-16T19:15:11.165249Z
K 7
svn:log
V 348
Add a guard for broken SUBDIR.${MK_FOO} use

Check for the variable SUBDIR. and error as it usually means someone
forgot to include src.opts.mk.

This guard from CheriBSD found the bugs in r367655 and r367728.

Reviewed by:	bdrewery, arichardson
Obtained from:	CheriBSD
Sponsored by:	DARPA
Differential Revision:	https://reviews.freebsd.org/D27211

END