Add buildtools/ to .gitignore

BUG=none
R=machenbach@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/312643004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21638 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Make dependencies target less noisy when run repeatedly

BUG=none
R=machenbach@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/309933005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21639 ce2b1a6d-e550-0410-aec6-3dcde31c8c00