cannot build to iOS: too many open files

to isolate the problem I nuked all the .cs in this project (old project that runs and builds well in 4.7, runs well in 5.33 but no build)

Spoiler: copious amount of cannot create FMOD in the console

Error: Cannot create FMOD::Sound instance for resource library/metadata/03/03b32505144304438a89762c07c1d0b6.resource, (File not found. )
UnityEditor.HostView:OnGUI()

Spoiler: too many open files

Exception: ExtractAssemblyTypeInfo: Failed to process /Applications/Unity/Unity.app/Contents/UnityExtensions/Unity/GUISystem/UnityEngine.UI.dll, System.IO.IOException: Too many open files
at System.IO.FileStream..ctor (System.String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, Boolean anonymous, FileOptions options) [0x00251] in

Spoiler: too many open files (at the end)

Could not start compilationIOException: Too many open files
System.IO.Directory.GetCurrentDirectory () (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.IO/Directory.cs:259)
System.IO.Path.InsecureGetFullPath (System.String path) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.IO/Path.cs:358)

 

775086

 

Posted a solution here!