(re-)move qt build specific dependency checks from generic paths

the check whether a module depends on itself should be done by the code
which *builds* modules, not which *uses* them.

the check whether a plugin tries to use itself seems kinda pointless in
the first place, so just remove it.

Change-Id: I89b357dae7d7979d131b6824f197e7088047272f
Reviewed-by: Andy Nichols <andy.nichols@theqtcompany.com>

mkspecs/features/qt.prf

@@ -76,11 +76,6 @@ for(ever) {
             next()
         }
 
-        target_qt:isEqual(TARGET, $$MODULE_NAME) {
-            warning("$$TARGET cannot have a QT$$var_sfx of $$QTLIB")
-            next()
-        }
-
         contains(MODULE_CONFIG, internal_module): \
             using_privates = true
         contains(MODULE_CONFIG, ltcg): \
@@ -349,11 +344,7 @@ for(QT_CURRENT_VERIFY, $$list($$QT_PLUGIN_VERIFY)) {
        QT_PLUGINPATH = $$eval(QT_PLUGIN.$${QTPLUG}.TYPE)
 
         # Generate the plugin linker line
-        target_qt:isEqual(TARGET, QTPLUG) {
-            warning($$TARGET cannot have a QTPLUGIN of $$QTPLUG)
-        } else {
-            QT_LINKAGE = -l$${QTPLUG}$$qtPlatformTargetSuffix()
-        }
+        QT_LINKAGE = -l$${QTPLUG}$$qtPlatformTargetSuffix()
 
         # Only link against plugin in static builds
         isEqual(QT_CURRENT_VERIFY, QTPLUGIN): {

mkspecs/features/qt_module.prf

@@ -53,6 +53,8 @@ internal_module: \
 else: \
     MODULE_DEPENDS = $$replace(QT, -private$, )
 MODULE_DEPENDS = $$unique(MODULE_DEPENDS)
+contains(MODULE_DEPENDS, $$MODULE): \
+    error("$$TARGET depends on itself.")
 
 contains(TARGET, QtAddOn.*): \
     MODULE_DEFINE = QT_ADDON_$${ucmodule}_LIB