Fix assembly labels on MacOS X64 to be LOCAL_LABEL

[davidwrighton]

Not doing this leads to the functions being carved up by the linker, which leads to incorrect behavior.

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[janvorli]

@davidwrighton what was the issue you were observing?

[davidwrighton]

@janvorli this was the reason for ... #128955 The linker ended up doing something remarkable. It mangled the function order and inserted padding which consisted of incb [%rax] instructions .... but it happened to order the functions such that the next function was another part of the VSD dispatch logic (not the part which was next in the assembly file, the last part) and it would reliably actually successfully dispatch after making a small corruption of a chunk of the g_resolveCache structure (from running the padding logic). I'm rather flabbergasted that it worked as well as it did.

[janvorli]

Oh, that's fun. Thanks for the details.

[janvorli]

LGTM, thank you!

[davidwrighton]

/ba-g The only tests which have not passed are the Windows arm64 tests, and they won't pass due to an infra issue.