Auto merge of #118810 - Kobzol:revert-mcp-510-bootstrap, r=nnethercote

Revert using MCP510 in bootstrap

This reverts commit 40c3d351ada5d991f7474ecc4bc6c9b976c656cb. The commit started dogfooding MCP510 to enable `lld` when building the compiler , but it broke tests, because we don't pass `-Zunstable-options` on enough places. This PR hotfixes that, and temporarily makes the "self-contained" option.. not very self-contained. I'll send a proper fix later, but I want to unblock rustc developres that use `lld` locally.

r? `@nnethercote` (who discovered the problem)