Add gdbinit to tools/ directory.
Add gdbinit to tools/ directory.

Suggested usage: echo "source /path/to/v8/tools/gdbinit" >> ~/.gdbinit

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/375503009

git-svn-id: f98b9d40cb02301bc76fa9e1b46ee668158567fd@22252 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh