build: restore compat with old NetBSD sh (re: 6eeafa1)

I'd used expansions of the form ${foo-} for compatibility with a
possible future use of 'set -u'/'set -o nounset'. However, on older
NetBSD sh (as still in use on sdf.org and sdf-eu.org), if foo is
unset, then empty removal is not performed as it should and even an
unquoted ${foo-} yields an empty field. So, to be compatible with
NetBSD sh, we cannot use expansions of that form in contexts where
empty removal is expected.

bin/package

@@ -115,7 +115,7 @@ command=${0##*/}
 case $(getopts '[-][123:xyz]' opt --xyz 2>/dev/null; echo 0$opt) in
 0123)	USAGE=$'
 [-?
-@(#)$Id: '$command$' (ksh 93u+m) 2024-07-04 $
+@(#)$Id: '$command$' (ksh 93u+m) 2024-07-10 $
 ]
 [-author?Glenn Fowler <[email protected]>]
 [-author?Contributors to https://github.com/ksh93/ksh]
@@ -548,7 +548,7 @@ SEE ALSO
   pkgadd(1), pkgmk(1), rpm(1), sh(1), tar(1), optget(3)
 
 IMPLEMENTATION
-  version         package (ksh 93u+m) 2024-07-04
+  version         package (ksh 93u+m) 2024-07-10
   author          Glenn Fowler <[email protected]>
   author          Contributors to https://github.com/ksh93/ksh
   copyright       (c) 1994-2012 AT&T Intellectual Property
@@ -3187,7 +3187,7 @@ make|view)
 	case $target in
 	'')	target="install" ;;
 	esac
-	eval capture \$\{MAMAKE_DEBUG_PREFIX-} mamake \$makeflags \$noexec \$target $assign
+	eval capture \$MAMAKE_DEBUG_PREFIX mamake \$makeflags \$noexec \$target $assign
 
 	case $HOSTTYPE in
 	darwin.*)
@@ -3376,7 +3376,7 @@ test)	# run all available default regression tests, using our newly compiled she
 	set -f
 	set -- ${args:-src}
 	cd "$1" || exit
-	capture ${MAMAKE_DEBUG_PREFIX-} mamake test
+	capture $MAMAKE_DEBUG_PREFIX mamake test
 	;;
 
 use)	# finalize the environment

src/cmd/INIT/mamake.c

@@ -27,7 +27,7 @@
  * coded for portability
  */
 
-#define RELEASE_DATE "2024-07-08"
+#define RELEASE_DATE "2024-07-10"
 static char id[] = "\n@(#)$Id: mamake (ksh 93u+m) " RELEASE_DATE " $\0\n";
 
 #if _PACKAGE_ast
@@ -2229,7 +2229,7 @@ static int update(Rule_t *r)
 	}
 
 	/* do */
-	append(buf, "${MAMAKE_DEBUG_PREFIX-} ");
+	append(buf, "$MAMAKE_DEBUG_PREFIX ");
 	append(buf, getval(state.vars, "MAMAKE"));
 	append(buf, " -C ");
 	append(buf, r->name);