Dockerfile: add gawk dependency
Dockerfile: add gawk dependency

This is needed to build glibc on CI

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