Don't set CC environment variable unless we use clang and/or ccache.
Don't set CC environment variable unless we use clang and/or ccache.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/7629012

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@96550 0039d316-1c4b-4281-b951-d872f2087c98

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