Git: Ignore .cxx intermediate output directory

[consp1racy]

This is produced by CMake e.g. in FFmpeg extension. The directory is created in projectDir rather than buildDir.

[microkatz]

Hello @consp1racy,

Thank you for creating a pull request to contribute to the project. We don't take any PR's into the release branch, only the main branch. If you could please fix that then that would be great. Thanks!

[consp1racy]

Hi @microkatz, my bad, fixed!