Qbs: fix QBS_APPS_DESTDIR with spaces

Change-Id: I23f2a51aef58143dd530a50c7df43bfb7bb573a8
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>

qtcreator.pro

@@ -52,7 +52,7 @@ exists(src/shared/qbs/qbs.pro) {
     }
     system("echo QBS_PLUGINS_INSTALL_DIR = $${QTC_PREFIX}/$${IDE_LIBRARY_BASENAME}/qtcreator >> $$qmake_cache")
     system("echo QBS_LIBRARY_DIRNAME = $${IDE_LIBRARY_BASENAME} >> $$qmake_cache")
-    system("echo QBS_APPS_DESTDIR = $${IDE_BIN_PATH} >> $$qmake_cache")
+    system("echo QBS_APPS_DESTDIR = $${maybe_backslash}\"$${IDE_BIN_PATH}$${maybe_backslash}\">> $$qmake_cache")
     system("echo QBS_APPS_INSTALL_DIR = $${QTC_PREFIX}/bin >> $$qmake_cache")
     system("echo CONFIG += qbs_no_dev_install >> $$qmake_cache")
 }