The generic parameter is unused, and so is `map`

The current webrender commit occasionally fails without a reason, and
the latest webrender commit is missing a dependency on our Windows
builders. It's not worth installing an extra dependency for cargotest,
and the spurious failure makes keeping this test not worth it.

…ikomatsakis

Track the finalizing node in the specialization graph

Fixes rust-lang#70419
Fixes rust-lang#70442

r? @eddyb

Miri: make backtrace function names and spans match up

Currently, Miri backtraces are a bit confusing:
```
error: Undefined Behavior: entering unreachable code
  --> tests/compile-fail/never_transmute_void.rs:10:11
   |
10 |     match v {} //~ ERROR  entering unreachable code
   |           ^ entering unreachable code
   |
   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
note: inside call to `f` at tests/compile-fail/never_transmute_void.rs:17:5
  --> tests/compile-fail/never_transmute_void.rs:17:5
   |
17 |     f(v); //~ inside call to `f`
   |     ^^^^
   = note: inside call to `main` at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:67:34
   = note: inside call to closure at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/rt.rs:52:73
   = note: inside call to closure at /home/r/.rustup/toolchains/miri/lib/rustlib/src/rust/src/libstd/sys_common/backtrace.rs:130:5
```
When reading this like a normal backtrace, one would expect that e.g. the backrace involves the "main" function at "libstd/rt.rs:67:34". But that is not actually where we are in the main function, that is *where the main function is called*.

This is not how backtraces are usually rendered (including e.g. with `RUST_BACKTRACE=1`). Usually we print next to each function name where inside that function the frame is currently executing, not where the *parent* frame is executing. With this PR and the Miri side at rust-lang/miri#1283, the backtrace now looks as follows:
```
error: Undefined Behavior: entering unreachable code
  --> tests/compile-fail/never_transmute_void.rs:10:11
   |
10 |     match v {} //~ ERROR entering unreachable code
   |           ^ entering unreachable code
   |
   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
   = note: inside `f` at tests/compile-fail/never_transmute_void.rs:10:11
note: inside `main` at tests/compile-fail/never_transmute_void.rs:17:5
  --> tests/compile-fail/never_transmute_void.rs:17:5
   |
17 |     f(v); //~ inside `main`
   |     ^^^^
   = note: inside closure at /home/r/src/rust/rustc/src/libstd/rt.rs:67:34
   = note: inside closure at /home/r/src/rust/rustc/src/libstd/rt.rs:52:73
   = note: inside `std::sys_common::backtrace::__rust_begin_short_backtrace::<[closure@DefId(1:6034 ~ std[87db]::rt[0]::lang_start_internal[0]::{{closure}}[0]::{{closure}}[0]) 0:&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe], i32>` at /home/r/src/rust/rustc/src/libstd/sys_common/backtrace.rs:130:5
```
Now function name and printed line numbers match up in the notes.

This code is partially shared with const-eval, so the change also affects const-eval: instead of printing what is being called at some span, we print which function/constant this span is inside.

With this, we can also remove the `span` field from Miri's stack frames (which used to track the *caller span* of that frame, quite confusing), and then get of a whole lot of `span` arguments that ultimately just served to fill that field (and as a fallback for `caller_location`, which however was never actually used).

r? @oli-obk

…-obk

rustc_target::abi: rename FieldPlacement to FieldsShape.

Originally suggested by @eddyb.

…test, r=Mark-Simulacrum

cargotest: remove webrender

The current webrender commit occasionally fails without a reason, and the latest webrender commit is missing a dependency on our Windows builders. It's not worth installing an extra dependency for cargotest, and the spurious failure makes keeping this test not worth it.

r? @Mark-Simulacrum

…an-DPC

clean up E0468 explanation

r? @Dylan-DPC

…k-Simulacrum

compiletest: don't use `std::io::stdout()`, as it bypasses `set_print`.

This PR undoes a change made during rust-lang#69916, which became unnecessary during review but was left in by accident, and which isn't correct due to `libtest` using `std::io::set_print`, which overwrites the `println!` behavior but *not* `writeln!(std::io::stdout(), ...)`.

The effect of using `writeln!(std::io::stdout(), ...)` was that the diff output would show *while* running the tests, instead of at the end, when failing tests are listed.

r? @Mark-Simulacrum cc @oli-obk