Fix bitselect for float/double types v2

We need to reinterpret float/double types as uint/ulong in order to
perform the bitwise operations.

This has been tested with piglit, OpenCV, and the ocl conformance tests.

v2:
  - Use vector operations rather than splitting vectors into scalar
    components.

Reviewed-by: Aaron Watry <awatry@gmail.com>
llvm-svn: 231373