Use automatic color option with the latest clang.

Bug: 18187181

Now that I checked in the latest prebuilts, clang will automatically use
color on terminals and no color on redirection to files or non-terminals.

Change-Id: I9be00c44947946cc18ce59c936b7f45d0ce2b6fc
Merge "Use automatic color option with the latest clang."
Merge remote-tracking branch 'upstream/master'