When clobbering a V8 make build, kill the entire output directory
When clobbering a V8 make build, kill the entire output directory

This will ensure that the generated Makefiles get removed as well

BUG=331475
TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/123673003

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@242876 0039d316-1c4b-4281-b951-d872f2087c98

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