test: Fix ENV.cxx11
test: Fix ENV.cxx11

ENV.cxx11 in a test block fails on Linux with
Error: ibex: failed
An exception occurred within a child process:
NoMethodError: undefined method `non_apple_gcc_version'
See for example brew test ibex on Linux.

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