Now that the Make Abstract Machine files are maintained manually
and not generated automatically, unused variables are an annoying
distraction -- and there are many.
But the language/format is very simple and very parseable using
shell, awk, etc. -- so this was easy to automate. All variables are
declared with 'setv' and they are used if an expansion of the form
${varname} exists (the braces are mandatory in Mamfiles).
bin/Mamfile_rm_unused_vars:
- Added for reference and future use.
src/*/*/Mamfile:
- Remove all unused 'setv' variable declarations.
