Fix single process build

A race condition triggered that sometimes the file
output/python/qgis/__init__.py was not created before a python uic
compiler started and therefore the required module could not be
imported.

This leads to errors like

[ 82%] Generating ui_dialogAbout.py
Traceback (most recent call last):
  File "../../../../../scripts/pyuic-wrapper.py", line 26, in <module>
    import qgis.PyQt.uic.pyuic
ImportError: No module named qgis.PyQt.uic.pyuic
python/plugins/GdalTools/tools/CMakeFiles/zzz-GdalTools-2-depend.dir/build.make:117:
recipe for target 'python/plugins/GdalTools/tools/ui_dialogAbout.py'
failed
make[2]: *** [python/plugins/GdalTools/tools/ui_dialogAbout.py] Error 1
CMakeFiles/Makefile2:5074: recipe for target
'python/plugins/GdalTools/tools/CMakeFiles/zzz-GdalTools-2-depend.dir/all'
failed
make[1]: ***
[python/plugins/GdalTools/tools/CMakeFiles/zzz-GdalTools-2-depend.dir/all]
Error 2
Makefile:160: recipe for target 'all' failed
make: *** [all] Error 2

python/PyQt/CMakeLists.txt

@@ -21,6 +21,7 @@ SET(PYQT_COMPAT_FILES
 )
 
 ADD_CUSTOM_TARGET(pyqtcompat ALL)
+ADD_DEPENDENCIES(pyqtcompat pyutils)
 
 IF(ENABLE_QT5)
   SET(PYQT_PREFIX PyQt5)