This patch does two things:
- Add compiler flag checks for -std=c++11 and -std=c++1y and remove check for -std=c++0x.
- Add configuration option LIBCXX_ENABLE_CXX1Y to prevent/allow -std=c++1y from being chosen as the std version. LIBCXX_ENABLE_CXX1Y is set to OFF by default.
- if LIBCXX_ENABLE_CXX1Y is enabled then set LIBCXX_STD_VERSION to c++1y and fail if the compiler does not support -std=c++1y
- If c++1y is not enabled then use c++11 and fail if the compiler does not support c++11.
- Update lit.site.cfg.in to capture LIBCXX_STD_VERSION information as config.std.
- Remove mentions of has_cxx0X configuration option.
- Check for `--param std=X' passed to lit on the command line.
- Choose the std for the tests either from command line parameter or (if it doesn't exist) the lit.site.cfg.