6296dd2bc4
GCC 4.9 only defines '__cplusplus' to the value 201300L and not to 201402L as expected for C++14. This makes the check for the available C++ standards in the interpreter fail to enable C++14 (which in turn means that ROOT cannot be compiled with GCC 4.9 if C++14 was enabled in Cmake). Similarly, for C++17 apart from the proper value 201703L other values seems to be floating around (e.g. 201406L as defined by the version of LLVM included with ROOT). The requirement for '__cplusplus_' to enable certain C++ standards in the interpreter is made less strict and just needs to be larger than the previous final value. This basically reinstates commit 0a62e34aa86b812651cfcf9526ba03b975adaa5c which was undone by commit 702298d9ad83866d0be62f0422c03ac8ea6687f1.