Introduce the KEEPKERNELS variable: if this is set either in mk.conf or
the environment, 'make cleandir' does not descend into kernel build
directories. Thus, kernel object files survive 'make build' on slower
architectures.

WARNING:
If you set this variable, you run the risk of breaking 'make release':
Be sure to run 'make cleandir' from /sys/arch/$(machine)/compile before
doing 'make release'. This issue will be addressed shortly.

requested by kettenis;
ok deraadt

Kernel builds now happen in compile/CONFIG/obj@ -> /usr/obj/... [or ./obj/,
if srctree is not rooted at /usr/src]. As a result, stock GENERIC & RAMDISK
kernels are commited to the tree, to ensure the src tree can be "readonly"
during builds, with all writes occuring inside the obj space. config -b
options are handled by ../Makefile.inc. The canonical new way to configure
one of these kernels is:
% cd /sys/arch/amd64/compile/GENERIC.MP
% doas make obj
% make config
% make
% doas cp obj/bsd /bsd
The build infrastructure will use this new mechanism in a de-escalation
way using BUILDUSER.
Much help from natano and tb.

fix arch/mach confusion in make tags. from frantisek holop

reflect reality, mark as NOOBJ
"sure" deraadt@

sync TDIRS with reality

"looks good" deraadt@

Push all potential (as in, all system MI not utilized by the bootblocks)
.h files into the ctags run as well to bring #define's and structs and
such into scope. Problem reported by thib

no need to specify the -t flag to ctags

Completely rewrite the tags file creation process. use config(8) against
a fat kernel (GERERIC or GENERIC.MP) into a temporary dir, then extract some
variables using make -V, and after some more singing and dancing use this
full and (more) correct list of files with ctags. Don't read this code.
ok guenther

Work in progress standalone boot blocks for OpenBSD/loongson systems. Will
load a kernel from the OpenBSD partition, with symbols.
However:
- does not work on gdium (usb i/o errors)
- no countdown due to PMON limitations, so either `bsd' in the PMON
environment contains a kernel filename to load, and it will get loaded
immediately, or it doesn't (e.g. the variable does no exist) and you get
a prompt and can pass options to the kernel. Note that /etc/boot.conf
commands can still be used in both cases.
- does not work for me when loaded automatically from PMON (put in the `al'
environment variable). However, `boot $al' works fine. Need to investigate.