Fix qbs build for qbs >= 1.10

Shadowing modules does no longer work from qbs 1.10 on; we need to give
our implementation of qbsbuildconfig a higher priority.

Change-Id: I703b780d564c43ebc2a4318f683537f10c4e5f3c
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

qbs/modules/qbsbuildconfig/qbsbuildconfig.qbs

@@ -4,6 +4,8 @@ import qbs.FileInfo
 Module {
     Depends { name: "qtc" }
 
+    property bool priority: 1 // TODO: Remove declaration after 1.11 is out.
+
     property bool enableUnitTests: false
     property bool enableProjectFileUpdates: true
     property bool installApiHeaders: false