math: Add frexp ported from amd-builtins

The float implementation is almost a direct port from the amd-builtins,
but instead of just having a scalar and float4 implementation, it has
a scalar and arbitrary width vector implementation.

The double scalar is also a direct port from AMD's builtin release.

The double vector implementation copies the logic in the float vector
implementation using the values from the double scalar version.

Both have been tested in piglit using tests sent to that project's
mailing list.

Signed-off-by: Aaron Watry <awatry@gmail.com>
Reviewed-by: Jan Vesely <jan.vesely@rutgers.edu>
llvm-svn: 260114