[zerocopy] Re-enable big endian aarch64 types

[197g]

When initially released the LLVM semantics did not agree with the intrinsics in the order of lanes and hence they got removed from stable on big endian targets. The fix of these semantics was shipped with Rust 1.87 in March 2025 (rust-lang/rust#136831).

To keep the library working in these previous compiler versions the intrinsics are enabled by their prior condition, a little endian target is detected, or the feature detection cfg of the more recent rust release is present.

Interesting point: the tests were never gated on target_endian = "little" so it seems that CI is not configured for any big endian aarch64 platform.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.85%. Comparing base (ff5ab2d) to head (70809e8).
⚠️ Report is 35 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3073      +/-   ##
==========================================
- Coverage   91.87%   91.85%   -0.02%     
==========================================
  Files          20       20              
  Lines        6057     6067      +10     
==========================================
+ Hits         5565     5573       +8     
- Misses        492      494       +2     

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[197g]

I don't know what it wants me to change in the CI file. Adding the new flag to the matrix is straightforward but the jobs/build_test/matrix/exclude section is odd. I suppose it should copy whatever is defined for no-zerocopy-aarch64-simd-1-59-0?

[jswrenn]

Thanks for this, and sorry for the late reply! Looks great, just a few small nits.

[jswrenn]

Suggested change

	#[cfg_attr(
	all(doc_cfg, target_endian = "little"),
	doc(cfg(rust = "1.59.0"))
	)]
	#[cfg_attr(
	doc_cfg,
	doc(cfg(all(target_arch = "aarch64", any(
	all(rust = "1.59.0", target_endian = "little"),
	rust = "1.87.0",
	))))
	)]

[197g]

Since I took those recommendations verbatim, I wanted to mark the commit with you in Co-Authored-By. It seems the CLA tool does not like it. How would you like me to refer to you?

[joshlf]

Try jswrenn@google.com or jack@wrenn.fyi? Not sure why since the email you used is in the recent Git history 🤷‍♂️

[jswrenn]

Factor out the target_arch = "aarch64"?

Suggested change

	#[cfg(any(
	all(target_arch = "aarch64", target_endian = "little"),
	all(target_arch = "aarch64", not(no_zerocopy_aarch64_simd_be_1_87_0))
	))]
	#[cfg(all(
	target_arch = "aarch64",
	any(
	target_endian = "little",
	not(no_zerocopy_aarch64_simd_be_1_87_0)
	)
	))]

[jswrenn]

Suggested change

	# 1.87.0 (#136831) the types were only correct on little endian and backed off
	# 1.87.0 (https://github.com/rust-lang/rust/pull/136831) the types were only correct on little endian and backed off