Unroll transcendentals benchmarks by 10x
Unroll transcendentals benchmarks by 10x

This reduces the overhead of the benchmark framework and calling the
routine. For example the results for rr::Cos vs. sw::Cos went from
9.6ns / 75ns to 75ns / 725ns. It illustrates that the timings did not
increase tenfold, and the gap between the two widened so it provides
a better measure of the achieved speedup as we further optimize these
transcendental SPIR-V instructions.

This change also copies the full result to an output buffer, to
ensure LLVM doesn't just compute the first element.

Bug: b/158231104
Change-Id: Ia9cde41b32559b16322d074767e986a68f00706d
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/62348
Kokoro-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Tested-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>

google/swiftshader,google/swiftshader,google/swiftshader