migrate run-pass/*/ to ui/run-pass

I think this is all that remains of #53764

migrate run-pass/borrowck to ui/run-pass

Part of #53764

Add unchecked_shl/shr check for intrinsics to fix miri's test suit

r? @RalfJung

cc @oli-obk

#53697 broke miri's test suite as described in [this comment](https://github.com/rust-lang/rust/pull/53697#issuecomment-419034668). This PR adds test for the `unchecked_shr/shl` for the intrinsics.

Remove `#[repr(transparent)]` from atomics

Added in #52149 the discussion in #53514 is showing how we may not want to
actually add this attribute to the atomic types. While we continue to
debate #53514 this commit reverts the addition of the `transparent` attribute.
This should be a more conservative route which leaves us the ability to tweak
this in the future but in the meantime allows us to continue discussion as well.

propagate build.python into cmake

If a suitable value of Python is not on `PATH`, one can still invoke x.py
manually, which propagates `BOOTSTRAP_PYTHON` into the bootstrap
environment.  But building LLVM will abort with error messages about not
being able to find Python, and instructions to set `PYTHON_EXECUTABLE`,
because nothing is done with `BOOTSTRAP_PYTHON` when invoking cmake.
Setting `build.python` in config.toml had no effect in this scenario,
either

To fix this, let's provide `PYTHON_EXECUTABLE` when invoking cmake; for
the "normal" case of Python in `PATH`, this doesn't alter any behavior.
For more unusual cases, however, this ensures cmake finds Python
properly.  (This change also ensures there are no differences between
what bootstrap is using, and what cmake uses, which may be useful for
consistency's sake.)

A few cleanups and minor improvements to mir/dataflow

- simplify `dot::GraphWalk::edges` and optimize its vector's allocation
- turn a `kill` loop into `kill_all`
- remove the `prepost` parameter from `dataflow_path` (it doesn't seem to do anything)
- a couple of other minor improvements

Add .git extension to submodule paths missing it

Fixes a problem where submodules could not be cloned under some git
configurations. Specifically, when url.git@github.com:.insteadOf =
https://github.com/ is set.

Minimized clippy test from when NLL disabled two-phase borrows

(Of course anyone even skimming the test will realize that this is an *expansion* of a previously posted [minimization](https://github.com/rust-lang/rust/issues/52934#issuecomment-418144787).)

Fix #52934.

Clarify `ManuallyDrop` docs

Mention that you can use `into_inner` to drop the contained value.

tidy: Cleanups and clippy warning fixes

This eliminates various clippy warnings in the tidy tool, as well as
making some related cleanups. These changes should not introduce any
functional differences.

Implement Unpin for Box, Rc, and Arc

Per the discussion in #49150, these should implement `Unpin` even if what they point to does not.

Migrate (some) of run-pass/ to ui

This is a step towards addressing #53764. Much still remains.

I went through a large portion of the `*.rs` files that were directly stored into `src/test/run-pass/` and moved them into various subdirectories of a newly created `src/test/ui/run-pass/`.

(yes, it would have perhaps been nice to meld it more directly with directories already in `src/test/ui/`; but the sad truth is that opens up the reality of filename collisions, and one of my short term goals for resolving #53764 is to keep the *filenames* invariant, even as their parents directories and contents are mildly revised...)

librustc_lint: In recursion warning, change 'recurring' to 'recursing'

The existing wording seems incorrect.

Aside: This warning, 'function cannot return without recursing' is not perfectly clear - it implies that the function _can_ return, it's just got to recurse. But really the fn cannot return period. Clearer wording: 'function recurses infinitely; it cannot return'; or 'function is infinitely self-recursive; it cannot return, and this is probably an error'. I like that.

Individual docs for {from,to}_*_bytes

Cross reference io::copy and fs::copy in docs.

Fixes https://github.com/rust-lang/rust/issues/52524.

Updated core/macros.rs to note it works in a no_std environment.

Fixes #45797
This PR updates the documentation of `write!` to note it works in a `no_std` environment, and adds an
example to showcase this. In a `no_std` environment, the author of the code is responsible for the
implementation of the `Write` trait. This example will work out of the box with `no_std`, but the
implementation of `Write` is expected to be provided by the user.

r? @steveklabnik

Update the compiler-builtins submodule

Fixes a mistake in using C shims to...

Closes #53916

rustc_resolve: allow `use crate_name;` under `uniform_paths`.

Specifically, `use crate_name;` and `use crate_name::{self, ...};` are now allowed, whereas previously there would produce a (false positive) ambiguity error, as the ambiguity detection code was seeing the `crate_name` import as a locally-available definition to conflict with the crate.

r? @petrochenkov cc @aturon @joshtriplett @Centril

Don't reduce E0161 to a warning in NLL migrate mode

This error has been on stable for a while, and allowing such code cause the compile to later ICE (since we can't codegen it). Errors `box UNSIZED EXPR` with unsized locals because it's not compatible with the current evaluation order (create the box before evaluating the expressions).

cc #53469 (fixes the ICE in this case)
cc @qnighy

Fix issue #52475: Make loop detector only consider reachable memory

As [suggested](https://github.com/rust-lang/rust/pull/51702#discussion_r197585664) by @oli-obk `alloc_id`s should be ignored by traversing all `Allocation`s in interpreter memory at a given moment in time, beginning by `ByRef` locals in the stack.

- [x] Generalize the implementation of `Hash` for `EvalSnapshot` to traverse `Allocation`s
- [x] Generalize the implementation of `PartialEq` for `EvalSnapshot` to traverse `Allocation`s
- [x] Commit regression tests

Fixes #52626
Fixes https://github.com/rust-lang/rust/issues/52849

Discussion can be found on rust-lang/rust#41620.

(or generics that *might* have dtors)

Just shuffling files here; the needed updates to content come later.

That is, opting to ignore stable `#![feature(..)]`, under my theory
that a reviewer would prefer as much stuff to be bucketed under "ah
another `#![allow(..)]` here." as possible.

See rust-lang/rust#34761.

Discussion can be found on rust-lang/rust#41620.