qdoc generated output test doesn't handle multi-config generators

When configuring with CMake and using a multi-config generator (Ninja Multi-Config in my case), CMake's generation phase fails with error messages like the following:

CMake Error in qttools/tests/auto/qdoc/generatedoutput/CMakeLists.txt:
  Evaluation file to be written multiple times with different content.  This
  is generally caused by the content evaluating the configuration type,
  language, or location of object files:

   /Users/craig/Projects/build/qt5/qttools/tests/auto/qdoc/generatedoutput/qdocincludepaths.inc

The framework header search paths contain a config-specific path, which makes the contents of the generated qdocincludepaths.inc file config-specific. This file needs to be changed to a set of config-specific files and the generated tst_generatedoutput.cpp file also needs to use the right one for the active build config instead of assuming a single file for all configs.