Check that /usr/bin/cc exists in `brew doctor`
Check that /usr/bin/cc exists in `brew doctor`

Refs Homebrew/homebrew#7454.
zmwangx/brew,mgrimes/brew,JCount/brew,muellermartin/dist,jmsundar/brew,Homebrew/brew,JCount/brew,reelsense/brew,mgrimes/brew,sjackman/homebrew,hanxue/linuxbrew,Homebrew/brew,jmsundar/brew,gordonmcshane/homebrew,staticfloat/brew,AnastasiaSulyagina/brew,mahori/brew,staticfloat/brew,rwhogg/brew,gordonmcshane/homebrew,DomT4/brew,maxim-belkin/brew,amar-laksh/brew_sudo,DomT4/brew,alyssais/brew,vitorgalvao/brew,vitorgalvao/brew,palxex/brew,alyssais/brew,Homebrew/brew,nandub/brew,maxim-belkin/brew,hanxue/linuxbrew,toonetown/homebrew,DomT4/brew,tonyg/homebrew,rwhogg/brew,nandub/brew,AnastasiaSulyagina/brew,sjackman/homebrew,EricFromCanada/brew,toonetown/homebrew,maxim-belkin/brew,DomT4/brew,bfontaine/brew,konqui/brew,pseudocody/brew,bfontaine/brew,gregory-nisbet/brew,nandub/brew,toonetown/homebrew,tonyg/homebrew,gregory-nisbet/brew,MikeMcQuaid/brew,Linuxbrew/brew,ilovezfs/brew,EricFromCanada/brew,gregory-nisbet/brew,aw1621107/brew,ilovezfs/brew,reitermarkus/brew,JCount/brew,vitorgalvao/brew,konqui/brew,muellermartin/dist,MikeMcQuaid/brew,pseudocody/brew,konqui/brew,claui/brew,mgrimes/brew,Homebrew/brew,gordonmcshane/homebrew,mistydemeo/homebrew,palxex/brew,aw1621107/brew,claui/brew,reitermarkus/brew,rwhogg/brew,EricFromCanada/brew,mahori/brew,reelsense/brew,reitermarkus/brew,bfontaine/brew,ilovezfs/brew,claui/brew,konqui/brew,reelsense/brew,aw1621107/brew,EricFromCanada/brew,palxex/brew,amar-laksh/brew_sudo,Linuxbrew/brew,zmwangx/brew,mahori/brew,staticfloat/brew,zmwangx/brew,vitorgalvao/brew,hanxue/linuxbrew,mistydemeo/homebrew,tonyg/homebrew,mistydemeo/homebrew,sjackman/homebrew,JCount/brew,muellermartin/dist,amar-laksh/brew_sudo,jmsundar/brew,Linuxbrew/brew,alyssais/brew,nandub/brew,MikeMcQuaid/brew,claui/brew,pseudocody/brew,AnastasiaSulyagina/brew,mahori/brew,Linuxbrew/brew,sjackman/homebrew,MikeMcQuaid/brew,reitermarkus/brew