…ther` has more than `i64::MAX` seconds

blessed new test

Our `Cursor::peek_prev` and `CursorMut::peek_prev` must agree
on how to behave when they are called on the "null element".

This is done to simplify to relationship between names() and values()
but also make thing clearer (having an Any to represent that any values
are allowed) but also to allow the (none) + values expected cases that
wasn't possible before.

Fix `checked_{add,sub}_duration` incorrectly returning `None` when `other` has more than `i64::MAX` seconds

Use `checked_{add,sub}_unsigned` in `checked_{add,sub}_duration` so that the correct result is returned when adding/subtracting durations with more than `i64::MAX` seconds.

…r-errors

Implement RFC 3348, `c"foo"` literals

RFC: rust-lang/rfcs#3348
Tracking issue: rust-lang#105723

Reduce MIR dump file count for MIR-opt tests

As referenced in issue rust-lang#109502 , mir-opt tests previously used the -Zdump-mir=all flag, which generates very large output.  This PR only dumps the passes under test, greatly reducing dump output.

Added default target cpu to `--print target-cpus` output and updated docs

Added default target cpu info as requested in issue rust-lang#110647 and noted the new output in the documentation

…trochenkov

Improve check-cfg implementation

This PR makes multiple improvements into the implementation of check-cfg, it is a prerequisite to a follow-up PR that will introduce a simpler and more explicit syntax.

The 2 main area of improvements are:
 1. Internal representation of expected values:
    - now uses `FxHashSet<Option<Symbol>>` instead of `FxHashSet<Symbol>`, it made the no value expected case only possible when no values where in the `HashSet` which is now represented as `None` (same as cfg represent-it).
    - a enum with `Some` and `Any` makes it now clear if some values are expected or not, necessary for `feature` and `target_feature`.
 2. Diagnostics: Improve the diagnostics in multiple case and fix case where a missing value could have had a new name suggestion instead of the value diagnostic; and some drive by improvements

I highly recommend reviewing commit by commit.

r? `@petrochenkov`

…-peek-prev, r=Amanieu

btree_map: `Cursor{,Mut}::peek_prev` must agree

Our `Cursor::peek_prev` and `CursorMut::peek_prev` must agree on how to behave when they are called on the "null element". This will fix rust-lang#111228.

r? `@Amanieu`