Two ARM64-specific compiler optimization bugs, in GCC 15/16 and Rust, hit curl

Not actually confirmed as compiler bugs yet.

Here’s a similar bug where OpenSSL’s inline asm was wrong and probably only GCC was smart enough to try to exploit the bug:

https://github.com/openssl/openssl/pull/23233

Same for rust - could be UB in quiche that is getting exposed.

The social post links to this bug https://github.com/curl/curl/issues/23237

Looks like a valid new optimization to me, which only fails on valgrind, which is a bit too strict with uninitialized values. In openssl's strlcpy. They'll deal with that.