Math Library Intrinsics as native intrinsics

Hi Micah,

There seems to be some math library functions that are already built
into llvm as intrinsic(pow, exp, etc...) but there are lots that are not
built in yet. Is there currently work going on that is implementing
these? I do not want to duplicate work so I want to see what is out
there.

another approach is to get rid of the llvm intrinsics, because they
don't buy you anything that you can't get with function attributes
and a list of libcalls.

The math functions that I will be adding in are from the following spec,
section 6.

Khronos OpenCL Registry - The Khronos Group Inc

Ciao,

Duncan.