NixOS puts Linux's dynamic loader in wierd place. Detect when we're on NixOS
and patch the downloaded bootstrap executables appropriately.

As per comment: #39297 (comment)

In the long run we want to separate out the dist builders from the test
builders. This provides us leeway to expand the dist builders with more tools
(e.g. Cargo and the RLS) without impacting cycle times.

Currently the Travis dist builders double-up the platforms they provide builds
for, so I figured we could try that out for MSVC as well. This commit adds a new
AppVeyor builder which runs a dist for all the MSVC targets:

* x86_64-pc-windows-msvc
* i686-pc-windows-msvc
* i586-pc-windows-msvc

If this takes too long and/or times out we'll need to split this up. In any case
we're going to need more capacity from AppVeyor no matter what becaue the two
pc-windows-gnu targets can't cross compile so we need at least 2 more builders
no matter what.

Refactor macro resolution errors + add derive macro suggestions

Move legacy macro resolution error reporting to `finalize_current_module_macro_resolutions`, and provide suggestions for derive macros.

Fixes #39323

cc #30197

r? @jseyfried

appveyor: Move MSVC dist builds to their own builder

In the long run we want to separate out the dist builders from the test
builders. This provides us leeway to expand the dist builders with more tools
(e.g. Cargo and the RLS) without impacting cycle times.

Currently the Travis dist builders double-up the platforms they provide builds
for, so I figured we could try that out for MSVC as well. This commit adds a new
AppVeyor builder which runs a dist for all the MSVC targets:

* x86_64-pc-windows-msvc
* i686-pc-windows-msvc
* i586-pc-windows-msvc

If this takes too long and/or times out we'll need to split this up. In any case
we're going to need more capacity from AppVeyor no matter what becaue the two
pc-windows-gnu targets can't cross compile so we need at least 2 more builders
no matter what.

Ignore expected type in diverging blocks

As per comment: #39297 (comment)

Fix for bootstrapping on NixOS

NixOS puts Linux's dynamic loader in wierd place. Detect when we're on NixOS and patch the downloaded bootstrap executables appropriately.