Add powi fo f16 and f128

[tgross35]

This will unblock adding support to compiler_builtins (rust-lang/compiler-builtins#614), which will then unblock adding tests for these new functions.

[rustbot]

r? @Mark-Simulacrum

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They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[tgross35]

@rustbot label +F-f16_and_f128

[tgross35]

r? @joboet since you were on the other PR before I switched the branch

[joboet]

Sorry, this is absolutely not my area of expertise.
r? libs

[Noratrieb]

@bors r+ rollup looks good

[bors]

📌 Commit 7685734 has been approved by Nilstrieb

It is now in the queue for this repository.

[bors]

⌛ Testing commit 7685734 with merge ddba1dc...

[bors]

☀️ Test successful - checks-actions
Approved by: Nilstrieb
Pushing ddba1dc to master...

[rust-timer]

Finished benchmarking commit (ddba1dc): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results (primary 0.6%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.6%, 0.6%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.6%	[0.6%, 0.6%]	1

Cycles

Results (primary -0.2%, secondary -0.4%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	6.1%	[6.1%, 6.1%]	1
Regressions ❌ (secondary)	2.2%	[1.8%, 2.9%]	4
Improvements ✅ (primary)	-3.3%	[-3.9%, -2.8%]	2
Improvements ✅ (secondary)	-2.4%	[-3.3%, -1.5%]	5
All ❌✅ (primary)	-0.2%	[-3.9%, 6.1%]	3

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 669.422s -> 667.526s (-0.28%)
Artifact size: 316.04 MiB -> 316.05 MiB (0.00%)