This patch makes GPU throughput benchmark results more comparable across
targets by disabling loop unrolling in the benchmark loop.

Motivation:
* PTX (post-LTO) evidence on NVPTX: for libc `sin`, the generated PTX
shows the `throughput` loop unrolled 8x at `N=128` (one iteration
advances the input pointer by 64 bytes = 8 doubles), interleaving eight
independent chains before the back-edge. This hides latency and
significantly reduces cycles/call as the batch size `N` grows.
* Observed scaling (NVPTX measurements): with unrolling enabled, `sin`
dropped from ~3,100 cycles/call at `N=1` to ~360 at `N=128`. After
enforcing `#pragma clang loop unroll(disable)`, results stabilized
(e.g., from ~3100 cycles/call at `N=1` to ~2700 at `N=128`).
* libdevice contrast: the libdevice `sin` path did not exhibit a similar
drop in our measurements, and the PTX appears as compact internal calls
rather than a long FMA chain, leaving less ILP for the outer loop to
extract.

What this change does:
* Applies `#pragma clang loop unroll(disable)` to the GPU `throughput()`
loop in both NVPTX and AMDGPU backends.

Leaving unrolling entirely to the optimizer makes apples-to-apples
comparisons uneven (e.g., libc vs. vendor). Disabling unrolling yields
fairer, more consistent numbers.

This patch provides cleanups and improvements for the GPU benchmarking
infrastructure. The key changes are:

- Fix benchmark convergence bug: Round up the scaled iteration count
(ceil) to ensure it grows properly. The previous truncation logic causes
the iteration count to get stuck.
- Resolve remaining compiler warning.
- Remove unused `BenchmarkLogger` files: This is dead code that added
maintenance and cognitive overhead without providing functionality.
- Improve build hygiene: Clean up headers and CMake dependencies to
strictly follow the 'include what you use' (IWYU) principle.

This patch improves the GPU benchmarking in this way:

* Replace `rand`/`srand` with a deterministic per-thread RNG seeded by
`call_index`: reproducible, apples-to-apples libc vs vendor comparisons.
* Fix input generation: sample the unbiased exponent uniformly in
`[min_exp, max_exp]`, clamp bounds, and skip `Inf`, `NaN`, `-0.0`, and
`+0.0`.
* Fix standard deviation: use an explicit estimator from sums and
sums-of-squares (`sqrt(E[x^2] − E[x]^2)`) across samples.
* Fix throughput overhead: subtract a loop-only baseline inside
NVPTX/AMDGPU timing backends so `benchmark()` gets cycles-per-call
already corrected (no `overhead()` call).
* Adapt existing math benchmarks to the new RNG/timing plumbing (plumb
`call_index`, drop `rand/srand`, clean includes).
* Correct inter-thread aggregation: use iteration-weighted pooling to
compute the global mean/variance, ensuring statistically sound `Cycles
(Mean)` and `Stddev`.
* Remove `Time / Iteration` column from the results table: it reported
per-thread convergence time (not per-call latency) and was
redundant/misleading next to `Cycles (Mean)`.
* Remove unused `BenchmarkLogger` files: dead code that added
maintenance and cognitive overhead without providing functionality.

---

## TODO (before merge)

* [ ] Investigate compiler warnings and address their root causes.
* [x] Review how per-thread results are aggregated into the overall
result.

## Follow-ups (future PRs)

* Add support to run throughput benchmarks with uniform (linear) input
distributions, alongside the current log2-uniform scheme.
* Review/adjust the configuration and coverage of existing math
benchmarks.
* Add more math benchmarks (e.g., `exp`/`expf`, others).

https://github.com/llvm/llvm-project/issues/149993

This PR adds benchmarking for `atan2()`, `__nv_atan2()`, and
`__ocml_atan2_f64()` using the same setup as `sin()`. This PR also adds
support for throughout bencmarking for functions with 2 inputs.

This PR implements
https://github.com/lntue/llvm-project/commit/2a158426d4b90ffaa3eaecc9bc10e5aed11f1bcf
to provide better throughput benchmarking for libc `sin()` and
`__nv_sin()`.

These changes have not been tested on AMDGPU yet, only compiled.

This PR adds sin benchmarking for a range of values and on a
pregenerated random distribution.

This is a part of #97655.

Reverts llvm/llvm-project#98075

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