For legacy reasons (presumably), Windows does not permit files name aux.

Instead of finding aux-build files in `auxiliary`, we now search for an
`aux` directory relative to the test. So if your test is
`compile-fail/foo.rs`, we would look in `compile-fail/aux`.  Similarly,
we ignore the `aux` directory when searching for tets.

Make the compiler emit an error if the crate graph contains two crates with the same crate-name and crate-salt but different SVHs.

This change is aimed at improving cross-crate (inlined) notation of generic
closures. The change modifies `simplify::where_predicates` to handle
parenthesized notation as well as starting to handle supertrait bounds as well.
This was necessary because all output constraints of closures are bound to
`FnOnce` but most trait bounds are that of `FnMut`.

Close #21801

With the addition of separate search paths to the compiler, it was intended that
applications such as Cargo could require a `--extern` flag per `extern crate`
directive in the source. The system can currently be subverted, however, due to
the `existing_match()` logic in the crate loader.

When loading crates we first attempt to match an `extern crate` directive
against all previously loaded crates to avoid reading metadata twice. This "hit
the cache if possible" step was erroneously leaking crates across the search
path boundaries, however. For example:

    extern crate b;
    extern crate a;

If `b` depends on `a`, then it will load crate `a` when the `extern crate b`
directive is being processed. When the compiler reaches `extern crate a` it will
use the previously loaded version no matter what. If the compiler was not
invoked with `-L crate=path/to/a`, it will still succeed.

This behavior is allowing `extern crate` declarations in Cargo without a
corresponding declaration in the manifest of a dependency, which is considered
a bug.

This commit fixes this problem by keeping track of the origin search path for a
crate. Crates loaded from the dependency search path are not candidates for
crates which are loaded from the crate search path.

As a result of this fix, this is a likely a breaking change for a number of
Cargo packages. If the compiler starts informing that a crate can no longer be
found, it likely means that the dependency was forgotten in your Cargo.toml.

[breaking-change]

Closes #17732
Closes #18819
Closes #19479
Closes #19631
Closes #19632
Closes #19850
Closes #19883
Closes #20005
Closes #20009
Closes #20389

The privacy pass of the compiler was previously not taking into account the
privacy of foreign items, or bindings to external functions. This commit fixes
this oversight by encoding the visibility of foreign items into the metadata for
each crate.

Any code relying on this will start to fail to  compile and the bindings must be
marked with `pub` to indicate that they can be used externally.

Closes #16725
[breaking-change]

Each test works by rendering the flowgraph for the last identified
block we see in expanded pretty-printed output, and comparing it (via
`diff`) against a checked in "foo.dot-expected.dot" file.

Each test post-processes the output to remove NodeIds ` (id=NUM)` so
that the expected output is somewhat stable (or at least independent
of how we assign NodeIds) and easier for a human to interpret when
looking at the expected output file itself.

----

Test writing style notes:

I usually tried to write the tests in a way that would avoid duplicate
labels in the output rendered flow graph, when possible.

The tests that have string literals "unreachable" in the program text
are deliberately written that way to remind the reader that the
unreachable nodes in the resulting graph are not an error in the
control flow computation, but rather a natural consequence of its
construction.

Signed-off-by: NDaniel Fagnan <dnfagnan@gmail.com>

This infrastructure is meant to support runnings tests that involve various
interesting interdependencies about the types of crates being linked or possibly
interacting with C libraries. The goal of these make tests is to not restrict
them to a particular test runner, but allow each test to run its own tests.

To this end, there is a new src/test/run-make directory which has sub-folders of
tests. Each test requires a `Makefile`, and running the tests constitues simply
running `make` inside the directory. The new target is `check-stageN-rmake`.

These tests will have the destination directory (as TMPDIR) and the local rust
compiler (as RUSTC) passed along to them. There is also some helpful
cross-platform utilities included in src/test/run-make/tools.mk to aid with
compiling C programs and running them.

The impetus for adding this new test suite is to allow various interesting forms
of testing rust linkage. All of the tests initially added are various flavors of
compiling Rust and C with one another as well as just making sure that rust
linkage works in general.

Closes #10434