Import bmake-20200710

Import bmake-20200710

from ChangeLog:

    o filemon/filemon_dev.c: use O_CLOEXEC rather than extra syscall
    o meta.c: target flagged .META is out-of-date if meta file missing
    o cond.c: fix for compare_expression when doEval=0
    o unit-tests/Makefile: rework
    o filemon/filemon_dev.c: ensure filemon fd is closed on exec.