Require --force to link keg-only.
Require --force to link keg-only.

Closes Homebrew/homebrew#13349.

konqui/brew,bfontaine/brew,aw1621107/brew,hanxue/linuxbrew,toonetown/homebrew,Linuxbrew/brew,jmsundar/brew,alyssais/brew,mahori/brew,sjackman/homebrew,muellermartin/dist,reitermarkus/brew,vitorgalvao/brew,mahori/brew,palxex/brew,staticfloat/brew,konqui/brew,tonyg/homebrew,konqui/brew,sjackman/homebrew,ilovezfs/brew,nandub/brew,MikeMcQuaid/brew,claui/brew,sjackman/homebrew,ilovezfs/brew,AnastasiaSulyagina/brew,reelsense/brew,amar-laksh/brew_sudo,JCount/brew,aw1621107/brew,staticfloat/brew,maxim-belkin/brew,reelsense/brew,palxex/brew,reitermarkus/brew,Homebrew/brew,Homebrew/brew,nandub/brew,rwhogg/brew,pseudocody/brew,hanxue/linuxbrew,staticfloat/brew,JCount/brew,EricFromCanada/brew,mistydemeo/homebrew,toonetown/homebrew,nandub/brew,mistydemeo/homebrew,muellermartin/dist,reitermarkus/brew,palxex/brew,bfontaine/brew,vitorgalvao/brew,vitorgalvao/brew,AnastasiaSulyagina/brew,tonyg/homebrew,tonyg/homebrew,alyssais/brew,MikeMcQuaid/brew,gordonmcshane/homebrew,aw1621107/brew,DomT4/brew,mgrimes/brew,Homebrew/brew,amar-laksh/brew_sudo,reitermarkus/brew,nandub/brew,gregory-nisbet/brew,maxim-belkin/brew,DomT4/brew,MikeMcQuaid/brew,mgrimes/brew,zmwangx/brew,mgrimes/brew,gregory-nisbet/brew,zmwangx/brew,jmsundar/brew,muellermartin/dist,jmsundar/brew,gordonmcshane/homebrew,claui/brew,gregory-nisbet/brew,claui/brew,bfontaine/brew,hanxue/linuxbrew,maxim-belkin/brew,DomT4/brew,rwhogg/brew,gordonmcshane/homebrew,mahori/brew,zmwangx/brew,AnastasiaSulyagina/brew,mahori/brew,reelsense/brew,Linuxbrew/brew,EricFromCanada/brew,Homebrew/brew,ilovezfs/brew,DomT4/brew,EricFromCanada/brew,pseudocody/brew,konqui/brew,EricFromCanada/brew,sjackman/homebrew,MikeMcQuaid/brew,vitorgalvao/brew,JCount/brew,rwhogg/brew,claui/brew,mistydemeo/homebrew,pseudocody/brew,JCount/brew,Linuxbrew/brew,amar-laksh/brew_sudo,alyssais/brew,toonetown/homebrew,Linuxbrew/brew