V8 Buildbot: Fix clobber feature for standalone builders.
V8 Buildbot: Fix clobber feature for standalone builders.

Because different directories are used in compile.py for compilation and for clobber, the feature was broken for all standalone builds.

This is a workaround fix that makes use of https://codereview.chromium.org/23003030/ to set the correct src dir.

Review URL: https://chromiumcodereview.appspot.com/23581002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@219773 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build