build_environment: tweak frozen string handling.
build_environment: tweak frozen string handling.

nandub/brew,nandub/brew,JCount/brew,sjackman/homebrew,EricFromCanada/brew,MikeMcQuaid/brew,claui/brew,Homebrew/brew,konqui/brew,konqui/brew,reitermarkus/brew,sjackman/homebrew,mahori/brew,sjackman/homebrew,JCount/brew,mahori/brew,claui/brew,vitorgalvao/brew,nandub/brew,Homebrew/brew,reitermarkus/brew,vitorgalvao/brew,vitorgalvao/brew,sjackman/homebrew,EricFromCanada/brew,JCount/brew,konqui/brew,claui/brew,reitermarkus/brew,MikeMcQuaid/brew,mahori/brew,konqui/brew,EricFromCanada/brew,vitorgalvao/brew,Homebrew/brew,mahori/brew,MikeMcQuaid/brew,Homebrew/brew,MikeMcQuaid/brew,nandub/brew,JCount/brew,claui/brew,EricFromCanada/brew,reitermarkus/brew