Does not handle incremental builds properly

[BrianDoig]

If you make a change and recompile the code, the Build Time Analyzer window updates the time, but it seems like it's not deleting the old results, and rather it is adding the new builds results to the last build. Line numbers don't update, and line counts increase rather than decreasing like what is reported.

Time for function before changes: 1202ms.
Incremental builds time reported after change: 1800ms. Time reported after clean and recompile: 52ms.

[phlippieb]

The following seems to work:

1. cd ~/Library/Developer/Xcode/DerivedData/<YOUR_APP>/Logs/Build
2. rm *.xcactivitylog
3. Build
4. Check build times again

UPDATE: Nope. It updates the build duration to the latest build's time, but the log still reflects the previous build.