build system: rm unused variable declarations from Mamfiles

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.

bin/Mamfile_rm_unused_vars

@@ -0,0 +1,30 @@
+#!/usr/bin/env sh
+IFS=''; set -fCu  # safe mode: no split/glob = no quoting headaches
+CCn='
+'  # newline
+let() { return $((!($1))); }
+
+# Remove unused variable definitions from a Mamfile.
+# Usage: Mamfile_rm_unused_vars <Mamfile >Mamfile.new
+#
+# Should work on all current POSIX compliant shells.
+# By Martijn Dekker <martijn@inlv.org>, 2021. Public domain.
+#
+# All variables are declared with 'setv' and they are used if an expansion
+# of the form ${varname} exists (the braces are mandatory in Mamfiles).
+
+mamfile=$(let $# && cat "$1" || cat)
+vars=$(printf '%s\n' $mamfile | awk '$1 == "setv" { print $2; }')
+rm_unused_ere=
+IFS=$CCn; for varname in $vars; do IFS=
+	case $mamfile in
+	*"\${$varname}"* )
+		;;
+	* )	# add with '|' separator for Extended Regular Expression
+		rm_unused_ere="${rm_unused_ere:+$rm_unused_ere|}setv[[:blank:]]+$varname([[:blank:]]|$)" ;;
+	esac
+done
+case $rm_unused_ere in
+'')	printf '%s\n' $mamfile ;;
+*)	printf '%s\n' $mamfile | grep -vE $rm_unused_ere ;;
+esac