Please provide the user-facing definitions of "struct _fpx_sw_bytes" and macros "FP_XSTATE_MAGIC2_SIZE", "FP_XSTATE_MAGIC1" and "FP_XSTATE_MAGIC2" to compile CoreCLR.

Related issue: https://github.com/dotnet/coreclr/issues/917#issuecomment-236907708

Usage:  https://github.com/dotnet/coreclr/blob/9585fc2/src/pal/src/include/pal/context.h#L142-L178