qb: Extend check_platform.

This extends the check_platform function to support checking more
than one OS for each feature.

This also adds the match helper function to qb.init.sh to compare
one variable against a list of variables.

qb/qb.init.sh

@@ -41,3 +41,19 @@ exists()
 	done
 	return $v
 }
+
+# match:
+# Compares a variable against a list of variables
+# $1 = variable
+# $@ = list of variables
+match()
+{
+	var="$1"
+	shift
+	for string do
+		case "$string" in
+			"$var" ) return 0 ;;
+		esac
+	done
+	return 1
+}

qb/qb.libs.sh

@@ -82,30 +82,45 @@ check_enabled()
 }
 
 # check_platform:
-# $1 = OS
+# $1 = OS ['OS' or 'OS OS2 OS3', $1 = name]
 # $2 = HAVE_$2
 # $3 = feature
-# $4 = enable feature when true [checked only if non-empty]
+# $4 = enable feature when 'true', disable errors with 'user' [checked only if non-empty]
 check_platform()
 {	tmpval="$(eval "printf %s \"\$HAVE_$2\"")"
 	[ "$tmpval" = 'no' ] && return 0
 
+	error=
+	newval=
 	setval="$(eval "printf %s \"\$USER_$2\"")"
 
-	if [ "$setval" = 'yes' ]; then
-		if { [ "$1" != "$OS" ] && [ "${4:-}" = 'true' ]; } ||
-				{ [ "$1" = "$OS" ] &&
-				[ "${4:-}" != 'true' ]; }; then
-			die 1 "Error: $3 not supported for $OS."
+	for platform in $(printf %s "$1"); do
+		if [ "$setval" = 'yes' ]; then
+			if [ "$error" != 'no' ] && [ "${4:-}" != 'user' ] &&
+					{ { [ "$platform" != "$OS" ] &&
+					match "${4:-}" true user; } ||
+					{ [ "$platform" = "$OS" ] &&
+					! match "${4:-}" true user; }; }; then
+				error='yes'
+			elif match "${4:-}" true user; then
+				error='no'
+			fi
+		elif [ "$platform" = "$OS" ]; then
+			if match "${4:-}" true user; then
+				newval=yes
+				break
+			else
+				newval=no
+			fi
+		elif match "${4:-}" true user; then
+			newval=auto
 		fi
-	elif [ "$1" = "$OS" ]; then
-		if [ "${4:-}" = 'true' ]; then
-			eval "HAVE_$2=yes"
-		else
-			eval "HAVE_$2=no"
-		fi
-	elif [ "${4:-}" = 'true' ]; then
-		eval "HAVE_$2="
+	done
+
+	if [ "${error}" = 'yes' ]; then
+		die 1 "Error: $3 not supported for $OS."
+	else
+		eval "HAVE_$2=\"${newval:-$tmpval}\""
 	fi
 }