refs #624 Use conditional SUBDIRS instead of REQUIRES for enabling/disabling subprojects.

src/src.pro

@@ -4,15 +4,33 @@ TEMPLATE = subdirs
 CONFIG += ordered
 
 SUBDIRS += blackmisc
-SUBDIRS += blacksound
-SUBDIRS += blackinput
-SUBDIRS += blackcore
-SUBDIRS += blackgui
-SUBDIRS += swiftguistandard
-SUBDIRS += swiftcore
-SUBDIRS += swiftdata
-SUBDIRS += swiftlauncher
-SUBDIRS += xbus
+contains(BLACK_CONFIG,BlackSound) {
+    SUBDIRS += blacksound
+}
+contains(BLACK_CONFIG,BlackInput) {
+    SUBDIRS += blackinput
+}
+contains(BLACK_CONFIG,BlackCore) {
+    SUBDIRS += blackcore
+}
+contains(BLACK_CONFIG,BlackGui) {
+    SUBDIRS += blackgui
+}
+contains(BLACK_CONFIG,SwiftGui) {
+    SUBDIRS += swiftguistandard
+}
+contains(BLACK_CONFIG,SwiftCore) {
+    SUBDIRS += swiftcore
+}
+contains(BLACK_CONFIG,SwiftData) {
+    SUBDIRS += swiftdata
+}
+contains(BLACK_CONFIG,SwiftLauncher) {
+    SUBDIRS += swiftlauncher
+}
+contains(BLACK_CONFIG,XPlane) {
+    SUBDIRS += xbus
+}
 SUBDIRS += plugins
 
 load(common_post)