Import bmake-20200902vendor/NetBSD/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 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.

1 files changed, 4 insertions, 0 deletions

diff --git a/unit-tests/lint.exp b/unit-tests/lint.exp
new file mode 100755
index 000000000000..9cd0eeb1ddf4
--- /dev/null
+++ b/unit-tests/lint.exp
@@ -0,0 +1,4 @@
+make: In the :@ modifier of "VAR", the variable name "${:Ubar:S,b,v,}" must not contain a dollar.
+y@:Q}
+xvaluey
+exit status 0