(cherry picked from commit 8beec62)

(cherry picked from commit f3e9dfa)

(cherry picked from commit 39f2d25)

This commit fixes several issues with the format string parsing of the
`#[diagnostic::on_unimplemented]` attribute that were pointed out by
@ehuss.
In detail it fixes:

* Appearing format specifiers (display, etc). For these we generate a
warning that the specifier is unsupported. Otherwise we ignore them
* Positional arguments. For these we generate a warning that positional
arguments are unsupported in that location and replace them with the
format string equivalent (so `{}` or `{n}` where n is the index of the
positional argument)
* Broken format strings with enclosed }. For these we generate a warning
about the broken format string and set the emitted message literally to
the provided unformatted string
* Unknown format specifiers. For these we generate an additional warning
about the unknown specifier. Otherwise we emit the literal string as
message.

This essentially makes those strings behave like `format!` with the
minor difference that we do not generate hard errors but only warnings.
After that we continue trying to do something unsuprising (mostly either
ignoring the broken parts or falling back to just giving back the
literal string as provided).

Fix rust-lang#122391

(cherry picked from commit 5568c56)

Errors started showing up, and I read somewhere that this might be
because of old ninja versions. This ninja version is indeed *ancient*.

```
multiple outputs aren't (yet?) supported by depslog; bring this up on the mailing list if it affects you
```

(cherry picked from commit b546764)