[1.0.21] build failure on aarch64

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See #1502

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This is a regression as 1.0.20 was OK
Of course, adding -flax-vector-conversions is a workaround (build + test suite OK)

Reproduced with GCC versions 11, 14, 15 and 16

[jedisct1]

Thanks!

New stable packages are out at https://download.libsodium.org/libsodium/releases/

[moubctez]

I would expect a new version.