Rollup merge of rust-lang#103379 - cuviper:truncate-thread-name, r=th…

…omcc

Truncate thread names on Linux and Apple targets

These targets have system limits on the thread names, 16 and 64 bytes
respectively, and `pthread_setname_np` returns an error if the name is
longer. However, we're not in a context that can propagate errors when
we call this, and we used to implicitly truncate on Linux with `prctl`,
so now we manually truncate these names ahead of time.

r? ``````@thomcc``````