Different behaviour of configure in qt5 and qtbase

1. Clone qt5 and qtbase:

   git clone --branch dev --depth 1 --shallow-submodules --recurse-submodules=qtbase git://code.qt.io/qt/qt5.git
   

2. If it's not merged yet, cherry-pick Andreas' fix to qtbase:

   cd qt5/qtbase
   git fetch "https://codereview.qt-project.org/qt/qtbase" refs/changes/35/321635/6 && git cherry-pick FETCH_HEAD
   

3. In a separate directory, try configure from qtbase:

   <parent>qt5/qtbase/configure -platform linux-clang -sanitize fuzzer-no-link
   

   This will succeed.

4. In another separate directory, try the same call with configure from qt5:

   <parent>qt5/configure -platform linux-clang -sanitize fuzzer-no-link
   

   This will fail:

   ERROR: Command line option -sanitize fuzzer-no-link is only supported with clang compilers.
   
   CMake Error at qtbase/cmake/QtBuildInformation.cmake:66 (message):
     Check the configuration messages for an error that has occurred.
   Call Stack (most recent call first):
     qtbase/cmake/QtBuildInformation.cmake:10 (qt_configure_print_summary)
     CMakeLists.txt:81 (qt_print_feature_summary)
   
   
   -- Configuring incomplete, errors occurred!
   See also "/tmp/bugreport1/CMakeFiles/CMakeOutput.log".
   See also "/tmp/bugreport1/CMakeFiles/CMakeError.log".
   CMake Error at /tmp/qt5/qtbase/cmake/QtProcessConfigureArgs.cmake:788 (message):
     CMake exited with code 1.
   

Both instances of configure should behave identically.