[dartdevc] fix build times by only linking input sources
[dartdevc] fix build times by only linking input sources

DDC was incorrectly re-linking transitive dependencies, so build times
continued to increase as the build progressed, with the application
itself performing the worst. With this fix, DDC is not on the critical
path and compiles are all very short.

Change-Id: Ia05bfb9f1a041fc979bc4bc0ee3bff9a0609b4b7
Reviewed-on: https://dart-review.googlesource.com/c/84966
Auto-Submit: Jenny Messerly <6285f43aa2dd0931180012d62b847adf2c37a418@google.com>
Reviewed-by: Jenny Messerly <6285f43aa2dd0931180012d62b847adf2c37a418@google.com>
Commit-Queue: Jenny Messerly <6285f43aa2dd0931180012d62b847adf2c37a418@google.com>

dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk