Simplify creation of `merged_headers`.
Simplify creation of `merged_headers`.

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