Rollup merge of #130477 - tmandry:revert-llvm-20-lto, r=tmandry

Revert #129749 to fix segfault in LLVM

This reverts commit 8c7a7e346be4cdf13e77ab4acbfb5ade819a4e60, reversing changes made to a00bd75b6c5c96d0a35afa2dc07ce3155112d278.

Reported in rust-lang/rust#129749 (comment). `@nikic's` theory is that the LLVM API changed in a way that makes it impossible to use concurrently from multiple threads (llvm/llvm-project#106427 (comment)). I pinged `@krasimirgg` who was fine with reverting.

r? `@rust-lang/wg-llvm`