This PR runs benchmarks on a 32 threads (A single warp on NVPTX) by
default, adding the option for single threaded benchmarks. We can
specify that a benchmark should be run on a single thread using the
`SINGLE_THREADED_BENCHMARK()` macro.
I chose to use a flag here so that other options could be added in the
future.
This PR replaces our old method of reducing the benchmark results by
using an array to using atomics instead. This should help us implement
single threaded benchmarks.
There was previously an issue where registering multiple benchmarks in
the same file would only give the results for the last benchmark to run.
This PR fixes the issue.
@jhuber6
PR for adding microbenchmarking infrastructure for NVPTX. `nvlink`
cannot perform LTO, so we cannot inline `libc` functions and this
function call overhead is not adjusted for during microbenchmarking.
