Merge bmake-20220330
Merge commit 'a052cb432096794be5070dc68a2b302eaf5a4783'

Update to bmake-20200902

Lots of code refactoring, simplification and cleanup.
Lots of new unit-tests providing much higher code coverage.
All courtesy of rillig at netbsd.

Other significant changes:

o new read-only variable .SHELL which provides the path of the shell
used to run scripts (as defined by the .SHELL target).

o variable parsing detects more errors.

o new debug option -dl: LINT mode, does the equivalent of := for all
variable assignments so that file and line number are reported for
variable parse errors.

Update to bmake-20200710

Key changes include reduced noise at end of failed build log
and avoid evaluation of unnecessary terms in conditionals.
In META MODE; a target flagged .META is out-of-date if meta file
is missing

MFC after: 1 week

Revert r363031

Update to bmake-20200704

Key changes include reduced noise at end of failed build log
and avoid evaluation of unnecessary terms in conditionals.

MFC after: 1 week

Merge bmake-20200517

Changes since 20181221 are mostly portability related
hence the large gap in versions imported.

There are however some bug fixes, and a rework of filemon handling.
In NetBSD make/filemon/filemon_ktrace.c allows use of fktrace
and elimination of filemon(4) which has not had the TLC it needs.

FreeBSD filemon(4) is in much better shape, so bmake/filemon/filemon_dev.c
allows use of that, with a bit less overhead than the ktrace model.

Summary of changes from ChangeLog

o str.c: empty string does not match % pattern
plus unit-test changes
o var.c: import handling of old sysV style modifier using '%'
o str.c: refactor brk_string
o meta.c: meta_oodate, CHECK_VALID_META is too aggressive for CMD
a blank command is perfectly valid.
o meta.c: meta_oodate, check for corrupted meta file
earlier and more often.
* meta.c: meta_compat_parent check for USE_FILEMON
patch from Soeren Tempel
o meta.c: fix compat mode, need to call meta_job_output()
o job.c: extra fds for meta mode not needed if using filemon_dev
o meta.c: avoid passing NULL to filemon_*() when meta_needed()
returns FALSE.
o filemon/filemon_{dev,ktrace}.c: allow selection of
filemon implementation. filemon_dev.c uses the kernel module
while filemon_ktrace.c leverages the fktrace api available in
NetBSD. filemon_ktrace.c can hopefully form the basis for
adding support for other tracing mechanisms such as strace on
Linux.
o meta.c: when target is out-of-date per normal make rules
record value of .OODATE in meta file.
o parse.c: don't pass NULL to realpath(3)
some versions cannot handle it.
o parse.c: ParseDoDependency: free paths rather than assert

plus more unit-tests

Merge bmake-20170510

No-op change other than version update.

Merge bmake-20160512

Merge bmake-20130123

Approved by: marcel (mentor)

Revert r363031