ARGV: fix build_head? call.
ARGV: fix build_head? call.

Fixes #6087.

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