I wanted to update mdbook's version. This ended up updating a bunch of other stuff too.

Addresses the second part of #42171 by removing the `TraitRef` from
`ProjectionTy`, and directly storing its `Substs`.

Closes #42171.

Prepare for `normalize-std???` which will share the same logic.
Added `ignore-32bit` and `ignore-64bit`.

Fixes #42879

regardless of context of attribute.

Extend the gating test to include the attribute in "weird" places.

Closes #43102

When copying libstd for the stage 2 compiler, the builder ignores the
configured libdir/libdir_relative configuration parameters.  This causes
the compiler to fail to find libstd, which cause any tools built with the
stage 2 compiler to fail.

To fix this, make the copy steps of rustbuild aware of the libdir_relative
parameter when the stage >= 2.  Also update the dist target to be aware of
the new location of libstd.

Fix some tests on Linux