Merging this PR will not alter performance

✅ 68 untouched benchmarks
⏩ 129 skipped benchmarks¹

_{Comparing yagiz/tune-tcmalloc (329a4a3) with main (02cf171)}

I think we'll need to select() based on //src/workerd/server:really_use_tcmalloc instead to handle the case of sanitizer builds (no tcmalloc but may be Linux) correctly. You may need to make that target public first for this to work.
Edit: Asan CI has passed – perhaps because we don't build benchmarks in the ASan job?

Edit: Asan CI has passed – perhaps because we don't build benchmarks in the ASan job?

Probably yes. Regardless, I've added the changes you recommended.