Do not perform a non-incremental compile when previous compile failed.

This reverts a not-fully-thought-out change to md5_check.py from
http://crrev.com/d8cef607861

Compiles fail for legitimate reasons, and we shouldn't delete md5
information in this case.

The concern behind that logic in the first case was that buggy --incremental
logic might be the reason for compile to fail. So, this commit also adds
a new environment variable to force all targets to be rebuilt:

FORCE_REBUILD=1

BUG=533442

Review URL: https://codereview.chromium.org/1374263002

Cr-Commit-Position: refs/heads/master@{#351345}


CrOS-Libchrome-Original-Commit: a1ae0267dc973f87eecc864485be03f91613b86d
1 file changed
tree: 9816f94349b53ec609463704aa6c477b6a62b35c
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/