formula: fix link_overwrite?
formula: fix link_overwrite?

Fixes #7921

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