Consider allowing errno and IEEE exception handling to be disabled by a define

[tannergooding]

It would be beneficial if __amd_raise_fp_exc could be be conditionally disabled by a define.

Certain environments, such as C#/.NET do not support IEEE floating-point exceptions and allowing this to be disabled could provide a slight advantage for the "error" cases.

This is likewise true in certain C/C++ configurations, such as for games, where the executed divsd will never fault.