Exclude unity source from visual studio scanning

[JasonDictos]

I've had this problem since forever with cotire, and the issue is when I generate my cmake solution, the unity generated files are in the output path, the same path that visual studio scans periodically. So when we clean, or rebuild once in a while we'll get these 'file is open' errors when it tries to clean the unity generated output.

e.g.

1>------ Skipped Clean: Project: all_unity, Configuration: Debug x64 ------
1>Project not selected to build for this solution configuration 
2>------ Skipped Clean: Project: clean_cotire, Configuration: Debug x64 ------
2>Project not selected to build for this solution configuration 
3>------ Skipped Clean: Project: ALL_BUILD, Configuration: Debug x64 ------
3>Project not selected to build for this solution configuration 
4>------ Clean started: Project: installer, Configuration: Debug Any CPU ------
5>------ Clean started: Project: app, Configuration: Debug Any CPU ------
6>------ Clean started: Project: webtest, Configuration: Debug Any CPU ------
7>------ Clean started: Project: engine_unity, Configuration: Debug x64 ------
8>------ Clean started: Project: engtest_unity, Configuration: Debug x64 ------
9>------ Clean started: Project: engtest, Configuration: Debug x64 ------
10>------ Clean started: Project: engine (engine\engine), Configuration: Debug x64 ------
11>------ Clean started: Project: engsup_unity, Configuration: Debug x64 ------
11>C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\IDE\VC\VCTargets\Microsoft.CppClean.targets(76,5): warning : The process cannot access the file 's:\code\aparavi-app\build\aparavi\engine\engsup\debug\cotire\engsup_cxx_prefix.hxx' because it is being used by another process.
11>Done building project "engsup_unity.vcxproj".
12>------ Clean started: Project: engsup, Configuration: Debug x64 ------
13>------ Skipped Clean: Project: ZERO_CHECK, Configuration: Debug x64 ------
13>Project not selected to build for this solution configuration 
========== Clean: 9 succeeded, 0 failed, 4 skipped ==========

Is there a good way to fix this?