turn on C++11 mode for cling when compiling with C++11 option.


git-svn-id: https://root.cern.ch/svn/root/trunk@48888 27541ba8-7e3a-0410-8455-c3a389f83636
Month "Dec" was truncated. Fixes issue #100892.


git-svn-id: https://root.cern.ch/svn/root/trunk@48890 27541ba8-7e3a-0410-8455-c3a389f83636