Set a default root only for the nacl builders, not naclports + gyp.
Set a default root only for the nacl builders, not naclports + gyp.

BUG=None
TEST=None
R=nodir@chromium.org,gdeepti@chromium.org

Review URL: https://codereview.chromium.org/1165773003

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@295541 0039d316-1c4b-4281-b951-d872f2087c98

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