Add CxxStdCompiledWith function that will error if C++ standard is unknown. Fix __float128 error for gcc with -std=c++1z.
Add CxxStdCompiledWith function that will error if C++ standard is unknown.
Fix __float128 error for gcc with -std=c++1z.

marsupial/cling,marsupial/cling,marsupial/cling,marsupial/cling,marsupial/cling,marsupial/cling