MFC r352929: Add a top-level makeman target

Abstracting away the details of how src.conf(5) is generated is arguably a
good thing; do so with a top-level makeman target.

MFC r340242:

Add a top-level make target to rebuild all sysent files.

The sysent target is useful when changing makesyscalls.sh, when
making paired changes to syscalls.master files, or in a future where
freebsd32 sysent entries are built from the default syscalls.master.

Reviewed by: bdrewery
Obtained from: CheriBSD
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D17899

MFC r320280,r320281,r320282,r320283,r320284,r320285,r320692,r322362,r322401,r322402,r336181:

r320280:
packages: Allow stageworld/stagekernel to run with make jobs.
r320281:
packages: Allow staging world/kernel in parallel.
r320282:
packages: Allow creating kernel/world packages in parallel.
r320283:
packages: Allow actually building individual world packages in parallel.
r320284:
packages: Parallelize individual kernel packaging.
r320285:
Expose only the create-packages-* targets since they set needed
DEST/DIRDIR.
r320692:
Fix create-kernel-packages with multiple BUILDKERNELS after r320284
r322362:
Indent nested conditionals for readability.
r322401:
Avoid creating kernel-dbg.txz distribution sets and kernel-debug packages
when MK_DEBUG_FILES is 'no'.
r322402:
Fix indentation from r322401.
r336181:
Fix parsing of create-kernel-packages

MFC r335708:

tinderbox: Give details about kernel builds.

MFC SVN r335750: Fix typo in top-level Makefile

Submitted by: Ben Widawsky <ben.widawsky@intel.com>
Sponsored by: Smule, Inc.
Differential Revision: https://reviews.freebsd.org/P186

MFC r330364:

Don't read SRC_ENV_CONF for MAKEOBJDIRPREFIX guard.

MFC r325627:

Deal with src.conf for top-level MAKEOBJDIRPREFIX guard.

MFC r319859, r319888:

Add support for "make universe_kernels -DMAKE_GENERIC_KERNELS" to build
just the GENERIC kernels for each arch (including variations such as
GENERIC-NODEBUG, GENERIC64, etc).
This helps with quickly doing a test build for all[*] arches without
building dozens of variant kernels for the arches that have lots of
hardware/board/system variations.
[*] Not all arches have a generic kernel (but they probably should for
test-building purposes, even if it can't boot on any real hardware).

By popular demand: change MAKE_GENERIC_KERNELS to MAKE_LINT_KERNELS.
It appears that the same arches that lack GENERIC kernel configs also lack
LINT. But enough different arches get built to ensure a kernel change
should build everywhere (32 and 64 bit, clang and old gcc, little and big
endian).

MFC r320273:

Allow ALWAYS_BOOTSTRAP_MAKE to force bmake bootstrapping.

MFC r316794:

Cache compiler metadata and reuse it at installworld time.

MFC r305147:

Add a 'make print-dir' that simply traverses all directories and prints them.

MFC r304006:

Avoid showing the bootstrap make command for check-old, etc.

MFC r303272,r303273:

r303272:
SYSTEM_COMPILER: Rework the logic to allow a 'make test-system-compiler'.
r303273:
Fix empty WANT_COMPILER_TYPE when neither compiler is bootstrapped.

Approved by: re (kib)