Fix some unaligned reads on SPARC in LTO

This fixes #43593 by eliminating some undefined behavior.

incr.comp.: Assert that no DepNode is re-opened (see issue #42298).

This PR removes the last occurrence of DepNode re-opening and adds an assertion that prevents our doing so in the future too. The DepGraph should no be guaranteed to be cycle free.

r? @nikomatsakis

EDIT: Closes https://github.com/rust-lang/rust/issues/42298

Link LLVM tools dynamically

Set `LLVM_LINK_LLVM_DYLIB=ON` -- "If enabled, tools will be linked with
the libLLVM shared library."  Rust doesn't ship any of the LLVM tools,
and only needs a few at all for some test cases, so statically linking
the tools is just a waste of space.  I've also had memory issues on
slower machines with LLVM debuginfo enabled, when several tools start
linking in parallel consuming several GBs each.

With the default configuration, `build/x86_64-unknown-linux-gnu/llvm`
was 1.5GB before, now down to 731MB.  The difference is more drastic
with `--enable-llvm-release-debuginfo`, from 28GB to "only" 13GB.

This does not change the linking behavior of `rustc_llvm`.

Add a more precise error message for issue #35976

When trying to perform static dispatch on something which derefs to a trait object, and the target trait is not in scope, we had confusing error messages if the target method had a `Self: Sized` bound. We add a more precise error message in this case: "consider using trait ...".

Fixes #35976.

r? @nikomatsakis

field does not exist error: note fields if Levenshtein suggestion fails

When trying to access or initialize a nonexistent field, if we can't infer what
field was meant (by virtue of the purported field in the source being a small
Levenshtein distance away from an actual field, suggestive of a typo), issue a
note listing all the available fields. To reduce terminal clutter, we don't
issue the note when we have a `find_best_match_for_name` Levenshtein
suggestion: the suggestion is probably right.

The third argument of the call to `find_best_match_for_name` is changed to
`None`, accepting the default maximum Levenshtein distance of one-third of the
identifier supplied for correction. The previous value of `Some(name.len())`
was overzealous, inappropriately very Levenshtein-distant suggestions when the
attempted field access could not plausibly be a mere typo. For example, if a
struct has fields `mule` and `phone`, but I type `.donkey`, I'd rather the
error have a note listing that the available fields are, in fact, `mule` and
`phone` (which is the behavior induced by this patch) rather than the error
asking "did you mean `phone`?" (which is the behavior on master). The "only
find fits with at least one matching letter" comment was accurate when it was
first introduced in 09d99247 (January 2015), but is a vicious lie in its
present context before a call to `find_best_match_for_name` and must be
destroyed (replacing every letter is within a Levenshtein distance of name.len()).

The present author claims that this suffices to resolve #42599.

Add MIR Validate statement

This adds statements to MIR that express when types are to be validated (following [Types as Contracts](https://internals.rust-lang.org/t/types-as-contracts/5562)). Obviously nothing is stabilized, and in fact a `-Z` flag has to be passed for behavior to even change at all.

This is meant to make experimentation with Types as Contracts in miri possible. The design is definitely not final.

Cc @nikomatsakis @aturon

Fix a number of failing tests on Solaris and SPARC

Implement AsRawFd for Stdin, Stdout, and Stderr

https://github.com/rust-lang/rfcs/issues/2074

This is a follow-up to f189d7a6 and 9d11b089.  While `-z ignore`
is what needs to be passed to the Solaris linker, because gcc is used as
the default linker, both that form and `-Wl,-z -Wl,ignore` (including
extra double quotes) need to be taken into account, which explains the
more complex regular expression.

This is a follow-up to ea23e50f, which fixed it for the build.

This fixes a handful of long-failing tests.

Thread docs fix and improvements.

None

Update nomicon

(This should have been in https://github.com/rust-lang/rust/pull/42959.)

Add regression test for #40510

This pull request adds a test case for issue #40510.

Fixes #40510.

When trying to perform static dispatch on something which derefs
to a trait object, and the target trait is not in scope, we had
confusing error messages if the target method had a
`Self: Sized` bound. We add a more precise error message in this
case: "consider using trait ...".

Fixes #35976.

extend config.toml doc for debug-assertions

Even after I knew that I had to change config.toml to get any printing from debug! and trace!, going over the entire fail did not make it clear to me that `debug-assertions` is the option controlling that.

Remove unused FnvHash code

None

Update RLS and deps

This PR further moves towards configuring save-analysis using the rls-data Config struct. We remove completely the concept of api_crate. Updates the RLS so the client is expecting these changes and which pulls in a commit re-enabling all RLS tests (been disabled due to a span error for a while).

Emphasise that these functions look at the disk, not just the path

I thought that `PathBuf::new("foo/bar/").is_dir()` is always true, because the path ends in `/`. However, this is not what `is_dir()` function does. So I've updated the docs to make it clear.

This fixes #43593 by eliminating some undefined behavior.

Remove unecessary test code #43219

related #43219

Improve hir::map::Map::get_parent_node doc

The documentation says
```
    /// Similar to get_parent, returns the parent node id or id if there is no
    /// parent.
    /// This function returns the immediate parent in the AST, whereas get_parent
    /// returns the enclosing item.
```
One would think that one can walk up the tree by repeatedly calling `get_parent_node` until it returns the argument, and then work on the `NodeId`s that arise. However, that is not true: `get_parent_node` will return id 0 (the crate itself) for items that sit directly in the crate; calling `get` on that `NodeId` will panic.

So, the fact that `get_parent_node` returns the root when passed the root is actually not really useful, because the root itself is already a somewhat degenerate node. This improves the doc so hopefully people writing code that "walks up the tree" don't run into this issue like I did...

incr.comp.: Properly incorporate symbol linkage and visibility into CGU hash.

This PR fixes the way the CGU hash for incr. comp. is computed. The CGU hash represents which `TransItems` are emitted into which codegen unit with which linkage and visibility. Before the new, LLVM-independent symbol internalizer the CGU hash did not accurately contain `TransItem` linkage and visibility because we would not enable symbol internalization in incremental mode anyway. The new internalizer is also run in incremental mode which uncovered the inaccuracy of CGU hashing. Luckily, the fix is rather simple.

r? @EddyB
cc @nikomatsakis