Currently the output on failure is as follows:

       Compiling block-buffer v0.10.4
       Compiling crypto-common v0.1.6
       Compiling digest v0.10.7
       Compiling sha2 v0.10.8
       Compiling xz2 v0.1.7
    error: failed to build archive: No such file or directory

    error: could not compile `bootstrap` (lib) due to 1 previous error

Print which file is being constructed to give some hint about what is
going on.

…d in import

When encountering a name in an import that could have come from a crate that wasn't imported, use a structured suggestion to suggest `extern crate foo;` pointing at the right place in the crate.

When encountering `_` in an import, do not suggest `extern crate _;`.

```
error[E0432]: unresolved import `spam`
  --> $DIR/import-from-missing-star-3.rs:2:9
   |
LL |     use spam::*;
   |         ^^^^ maybe a missing crate `spam`?
   |
help: consider importing the `spam` crate
   |
LL + extern crate spam;
   |
```

remove an unused boolean and then merge two big matches into one

…r=BoxyUwU

When an archive fails to build, print the path

Currently the output on failure is as follows:

       Compiling block-buffer v0.10.4
       Compiling crypto-common v0.1.6
       Compiling digest v0.10.7
       Compiling sha2 v0.10.8
       Compiling xz2 v0.1.7
    error: failed to build archive: No such file or directory

    error: could not compile `bootstrap` (lib) due to 1 previous error

Change this to print which file is being constructed, to give some hint about what is going on.

    error: failed to build archive at `path/to/output`: No such file or directory

…etrochenkov

Structured suggestion for `extern crate foo` when `foo` isn't resolved in import

When encountering a name in an import that could have come from a crate that wasn't imported, use a structured suggestion to suggest `extern crate foo;` pointing at the right place in the crate.

When encountering `_` in an import, do not suggest `extern crate _;`.

```
error[E0432]: unresolved import `spam`
  --> $DIR/import-from-missing-star-3.rs:2:9
   |
LL |     use spam::*;
   |         ^^^^ maybe a missing crate `spam`?
   |
help: consider importing the `spam` crate
   |
LL + extern crate spam;
   |
```

…riddle

nested aux-build in tests/rustdoc/ tests

* Fixes bug that prevented using nested aux-build in `tests/rustdoc/` tests. Before, `fn document` and the auxiliary builder disagreed about where to find the nested aux-build source file (`auxiliary/auxiliary/aux.rs` vs `auxiliary/aux.rs`), preventing them from building. Picked the latter in line with other builders in compiletest.
* Adds `//@ doc-flags` header, which forwards flags to rustdoc and not rustc.
* Adds `//@ unique-doc-out-dir` header, which sets the --out-dir for the rustdoc invocation to a unique directory: `<root out dir>/docs/<test name>/doc`
* Changes working directory of the rustdoc invocation to the root out directory (common among all aux-builds). Prior art: exec_compiled_test in runtest.rs
* Adds tests that use nested aux builds and new headers

These changes provide useful capabilities for writing rustdoc tests on their own. They are also needed to test the implementation for the [mergable-rustdoc-cross-crate-info](rust-lang/rfcs#3662) RFC.

More detailed note to deprecate ONCE_INIT

…-windows-abi, r=tgross35

Match LLVM ABI in `extern "C"` functions for `f128` on Windows

As MSVC doesn't support `_Float128`, x86-64 Windows doesn't have a defined ABI for `f128`. Currently, Rust will pass and return `f128` indirectly for `extern "C"` functions. This is inconsistent with LLVM, which passes and returns `f128` in XMM registers, meaning that e.g. the ABI of `extern "C"` compiler builtins won't match. This PR fixes this discrepancy by making the x86-64 Windows `extern "C"` ABI pass `f128` directly through to LLVM, so that Rust will follow whatever LLVM does. This still leaves the difference between LLVM and GCC (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054) but this PR is still an improvement as at least Rust is now consistent with it's primary codegen backend and compiler builtins from `compiler-builtins` will now work.

I've also fixed the x86-64 Windows `has_reliable_f16` match arm in `std` `build.rs` to refer to the correct target, and added an equivalent match arm to `has_reliable_f128` as the LLVM-GCC ABI difference affects both `f16` and `f128`.

Tracking issue: rust-lang#116909

try-job: x86_64-msvc
try-job: x86_64-mingw

…errors

Attribute checking simplifications

remove an unused boolean and then merge two big matches into one

I was reviewing some attributes and realized we don't really check this list against the list of builtin attributes, so we "may" totally be missing some attributes that we should be checking (like the `coroutine` attribute, which you can just apply to random stuff)

```rust
#![feature(coroutines)]
#[coroutine]
struct Foo;
```

just compiles for example. Unless we check that the fallthrough match arm is never reached for builtin attributes, we're just going to keep forgetting to add them here, too. I can do that without the changes in this PR, but it seemed like a nice cleanup