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-Original-Commit-Position: refs/heads/master@{#420752}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 0dfb6ba0b31eae8c8d2aab54ece37bb9ae29e9ea