Rollup merge of #35663 - CryZe:no-stdlib, r=Manishearth

Improve `No stdlib` and related Documentation

This renames all lang item function names to the ones used in `libstd` and `libpanic_unwind`. It also explains the `eh_unwind_resume` lang item in the `libcore` documentation, where it was missing. A third function is also needed on certain compilation targets, so this was also added to the `No stdlib` documentation.

diff --cc src/libcore/lib.rs
Simple merge