…Solaris

See ip(4P) man page:
 IP_MULTICAST_TTL     Time  to live for multicast datagrams. This option
                      takes an unsigned character as  an  argument.  Its
                      value  is  the TTL that IP uses on outgoing multi-
                      cast datagrams. The default is 1.

 IP_MULTICAST_LOOP    Loopback for multicast datagrams. Normally  multi-
                      cast  datagrams  are  delivered  to members on the
                      sending  host  (or  sending  zone).  Setting   the
                      unsigned  character argument to 0 causes the oppo-
                      site behavior, meaning that  when  multiple  zones
                      are  present,  the  datagrams are delivered to all
                      zones except the sending zone.

https://docs.oracle.com/cd/E88353_01/html/E37851/ip-4p.html
https://man.openbsd.org/ip.4

This reverts commit fd4a6a1.

…Simulacrum

Simplify NodeHeader by avoiding slices in BTreeMaps with shared roots

Simplify a complicated piece of code that creates slices of keys in node leaves.

…t-out, r=oli-obk

Implement `?const` opt-out for trait bounds

For now, such bounds are treated exactly the same as unprefixed ones in all contexts. [RFC 2632](rust-lang/rfcs#2632) does not specify whether such bounds are forbidden outside of `const` contexts, so they are allowed at the moment.

Prior to this PR, the constness of a trait bound/impl was stored in `TraitRef`. Now, the constness of an `impl` is stored in `ast::ItemKind::Impl` and the constness of a bound in `ast::TraitBoundModifer`. Additionally, constness of trait bounds is now stored in an additional field of `ty::Predicate::Trait`, and the combination of the constness of the item along with any `TraitBoundModifier` determines the constness of the bound in accordance with the RFC. Encoding the constness of impls at the `ty` level is left for a later PR.

After a discussion in \#wg-grammar on Discord, it was decided that the grammar should not encode the mutual exclusivity of trait bound modifiers. The grammar for trait bound modifiers remains `[?const] [?]`. To encode this, I add a dummy variant to `ast::TraitBoundModifier` that is used when the syntax `?const ?` appears. This variant causes an error in AST validation and disappears during HIR lowering.

cc rust-lang#67794

r? @oli-obk

Options IP_MULTICAST_TTL and IP_MULTICAST_LOOP are 1 byte on BSD

Options IP_MULTICAST_TTL and IP_MULTICAST_LOOP are 1 byte on BSD and Solaris

See ip(4P) man page:
 IP_MULTICAST_TTL     Time  to live for multicast datagrams. This option
                      takes an unsigned character as  an  argument.  Its
                      value  is  the TTL that IP uses on outgoing multi-
                      cast datagrams. The default is 1.

 IP_MULTICAST_LOOP    Loopback for multicast datagrams. Normally  multi-
                      cast  datagrams  are  delivered  to members on the
                      sending  host  (or  sending  zone).  Setting   the
                      unsigned  character argument to 0 causes the oppo-
                      site behavior, meaning that  when  multiple  zones
                      are  present,  the  datagrams are delivered to all
                      zones except the sending zone.

https://docs.oracle.com/cd/E88353_01/html/E37851/ip-4p.html
https://man.openbsd.org/ip.4

…xcrichton

Actually pass target LLVM args to LLVM

Missed in rust-lang#68059

r? @alexcrichton

check_match: misc unifications and ICE fixes

These are some unifications made as a by-product of working on `hir::ExprKind::Let`.

Fixes rust-lang#68396.
Fixes rust-lang#68394.
Fixes rust-lang#68393.

r? @oli-obk @matthewjasper

tidy: fix most clippy warnings

…etroalbini

lowering: cleanup some hofs

Some drive-by cleanup while working on `let_chains`.

r? @pietroalbini