Components named "system" shadow /usr/lib/libSystem.dylib on OS X.
Give the component a different output name, and also add an action for
a while that cleans up libsystem.dylib from existing build dirs.

BUG=649696

Review-Url: https://codereview.chromium.org/2362233003
Cr-Commit-Position: refs/heads/master@{#420752}