Qt5 macOS builds failing on Bitrise — missing /usr/local/.//mkspecs/macx-clang

[1ec5]

Starting today, the Qt5 macOS build bot on Bitrise consistently fails on all branches with the following error:

[Mason] Unpacking package to mason_packages/headers/polylabel/1.0.2...
CMake Error at /usr/local/lib/cmake/Qt5Core/Qt5CoreConfig.cmake:15 (message):
  The imported target "Qt5::Core" references the file

     "/usr/local/.//mkspecs/macx-clang"

  but this file does not exist.  Possible reasons include:

  * The file was deleted, renamed, or moved to another location.

  * An install or uninstall procedure did not complete successfully.

  * The installation package was faulty and contained

     "/usr/local/lib/cmake/Qt5Core/Qt5CoreConfigExtras.cmake"

  but not all the files it references.

Call Stack (most recent call first):
  /usr/local/lib/cmake/Qt5Core/Qt5CoreConfigExtras.cmake:50 (_qt5_Core_check_file_exists)
  /usr/local/lib/cmake/Qt5Core/Qt5CoreConfig.cmake:141 (include)
  platform/qt/qt5.cmake:1 (find_package)
  platform/qt/qt.cmake:82 (include)
  platform/qt/config.cmake:1 (include)
  CMakeLists.txt:80 (include)


-- Configuring incomplete, errors occurred!
See also "/Users/vagrant/git/build/qt-macos-x86_64/Debug/CMakeFiles/CMakeOutput.log".
make: *** [build/qt-macos-x86_64/Debug/build.ninja] Error 1

==> Script finished with exit code: 2

/ref #6716
/cc @brunoabinader @boundsj

[1ec5]

#6716 added a call to brew list --versions qt5. This weekend’s stack update doesn’t list any relevant changes, but bitrise-io/bitrise.io@27e59aa shows that Homebrew was upgraded from Homebrew/homebrew-core@484208f to Homebrew/homebrew-core@2ed6d8d. The qt5 formula was renamed qt in Homebrew/homebrew-core@b92c519.