fix for COMPILER-8891: std::exception::what() should not return NULL
fix for COMPILER-8891: std::exception::what() should not return NULL

vegard/libcxxrt,vegard/libcxxrt,xin3liang/platform_external_libcxxrt,cemeyer/libcxxrt,sudosurootdev/external_libcxxrt,xin3liang/platform_external_libcxxrt,sudosurootdev/external_libcxxrt,xin3liang/platform_external_libcxxrt,vegard/libcxxrt,sudosurootdev/external_libcxxrt,cemeyer/libcxxrt,cemeyer/libcxxrt