bsd.confs.mk: Support CONFGROUPS.yes

[ivy]

Summary

Align CONFGROUPS with other options like SUBDIRS and FILESGROUPS by
supporting the CONFGROUPS.yes option. This means logic like this:

.if ${MK_FOO} != "no"
CONFGROUPS+= FOO
.endif

can be replaced by:

CONFGROUPS.${MK_FOO}+= FOO

Use this to simplify libexec/rc/rc.d/Makefile, and while here, indent
and alphabetise the file.

MFC after: 1 week

[imp]

I'd commit bsd.conf.mk as its own commot. I did this to subdirs years ago

[ivy]

In D52923#1209241, @imp wrote:

I'd commit bsd.conf.mk as its own commot. I did this to subdirs years ago

i could split this into two commits if you insist, but i'd rather not. the changes to both files are self-contained, so it will look fine in the history.

[imp]

In D52923#1209247, @ivy wrote:

In D52923#1209241, @imp wrote:

I'd commit bsd.conf.mk as its own commot. I did this to subdirs years ago

i could split this into two commits if you insist, but i'd rather not. the changes to both files are self-contained, so it will look fine in the history.

But if another file uses this construct and then we find a problem in rc.d/makefile, it becomes harder to cleanly back that out since we have to either back out more things, or do a hacky diff to revert.

[ivy]

remove libexec/rc/rc.d changes