ENV.rb: Modifier methods accept lists of flags
ENV.rb: Modifier methods accept lists of flags

`ENV` methods that modify environment variables, `prepend`, `append` and
`remove`, can now accept lists of flags as well as a single flag.

The list of flags affected by `append_to_cflags` and `remove_from_cflags` are
now definied in a shortcut method `cc_flag_vars`.

Signed-off-by: Charlie Sharpsteen <828d338a9b04221c9cbe286f50cd389f68de4ecf@sharpsteen.net>

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