Set CC=clang as repo_env
Set CC=clang as repo_env

Setting it as action_env is wasteful as it is added to every action,
even though we only use it to select a compiler for the auto-
configured toolchain.

CodeIntelligenceTesting/jazzer,CodeIntelligenceTesting/jazzer,CodeIntelligenceTesting/jazzer,CodeIntelligenceTesting/jazzer,CodeIntelligenceTesting/jazzer