Auto merge of #88765 - mk12:update-llvm, r=cuviper

Update LLVM submodule

This merges upstream `release/13.x` changes to our fork. In particular,
this includes the bugfix https://reviews.llvm.org/D108608 (see also
https://bugs.llvm.org/show_bug.cgi?id=51637).

The motivation for this is fixing Rust coverage in Fuchsia: https://fxbug.dev/77427.

llvm-project @ 86c7daa6

-Subproject commit ec995b75d71c5f3b9a82fe084259477eb22f74da
+Subproject commit 86c7daa627aefda1371568b948eba21edf720747