Xcode builds are getting blocked when you have a large amount of dependencies

I was working with some Apple Engineers today but we ran out of time in the session. They asked that I post the feedback number with some information: FB7763992.

We were trying to figure out why I was having slow incremental compilation. In our testing, we found 1.4gb of .d files - the Apple Engineer believed the processing of these files slowed down the Xcode build process.