Auto merge of #41168 - Shizmob:jemalloc-musl, r=alexcrichton

Auto merge of #41168 - Shizmob:jemalloc-musl, r=alexcrichton

Fix jemalloc support for musl

Just like DragonFlyBSD, using the same symbols as the system allocator will result in a segmentation fault at runtime due to allocator mismatches. As such, it's better to prefix the jemalloc symbols instead, avoiding crashes.

We encountered this problem on a dynamically-linked musl target (with patches to Rust to make that possible, see #40113). It may not show up immediately obviously on the current statically-linked CRT targets.