Co-authored-by: jyn <[email protected]>

…ingw-w64, r=petrochenkov

Add `-lmingwex` second time in `mingw_libs`

Upcoming mingw-w64 releases will contain small math functions refactor which moved implementation around. As a result functions like `lgamma`
now depend on libraries in this order:
`libmingwex.a` -> `libmsvcrt.a` -> `libmingwex.a`.

Fixes rust-lang#124221

ignore generics args in attribute paths

Fixes rust-lang#97006
Fixes rust-lang#123911
Fixes rust-lang#123912

This patch ensures that we no longer have to handle invalid generic arguments in attribute paths.

r? `@petrochenkov`

bootstrap: add comments for the automatic dry run

reachable computation: extend explanation of what this does, and why

Follow-up to rust-lang#122769. I had the time to think about this some more, in particular in the context of rust-lang#119214, so I felt it was worth extending these comments some more.

I also gave up on the context of "externally reachable" as it is not called that way anywhere else in the compiler.

Cc `@tmiasko` `@saethlin`

…rochenkov

Make sure we consume a generic arg when checking mistyped turbofish

When recovering un-turbofish-ed args in expr position (e.g. `let x = a<T, U>();` in `check_mistyped_turbofish_with_multiple_type_params`, we used `parse_seq_to_before_end` to parse the fake generic args; however, it used `parse_generic_arg` which *optionally* parses a generic arg. If it doesn't end up parsing an arg, it returns `Ok(None)` and consumes no tokens. If we don't find a delimiter after this (`,`), we try parsing *another* element. In this case, we just infinitely loop looking for a subsequent element.

We can fix this by making sure that we either parse a generic arg or error in `parse_seq_to_before_end`'s callback.

Fixes rust-lang#124897