mimalloc: update to 3.2.8.

[jason1987d]

Testing the changes

• I tested the changes in this PR: briefly

Local build testing

• I built this PR locally for my native architecture, x86_64-libc
• I built this PR locally for these architectures (if supported. mark crossbuilds):
  • i686-libc

[jason1987d]

Does mold now work well with mimalloc 3.x? I notice that mold-2.40.4 changelog explicitly mentioned that they reverted mimalloc to 2.x due to stability issue.

Well, the current version in void's repositories is 2.34.1. I'll pay attention to the more recent versions of mold to see if anything gets updated with their usage of mimalloc.

Also finding that mold bundles its own mimalloc anyway.

[leahneukirchen]

Please rebase.

[cinerea0]

Superseded by #59483.