bin/brew: avoid unnecessary 'readlink' invocation
bin/brew: avoid unnecessary 'readlink' invocation

For typical installations where `brew` is not a symbolic link, this
reduces the number of processes that need to be spawned.

Closes Homebrew/homebrew#46269.

Signed-off-by: Martin Afanasjew <54669547a225ff20cba8b75a4adca540eef25858@afanasjew.de>

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