Upgrade `log` to `0.4` in multiple crates.

Refs #46437 as it also removes LLVMRustWriteDebugLocToString()

Refs #46437

The same effect can be achieved using -Cllvm-args=-debug

Refs #46437 as it removes LLVMRustSetDebug()

This `horizontal_trim` function strips the leading whitespace from
doc-comments that have a left-asterisk-margin:

  /**
   * You know what I mean—
   *
   * comments like this!
   */

The index of the column of asterisks is `i`, and if trimming is deemed
possible, we slice each line from `i+1` to the end of the line. But if, in
particular, `i` was 0 _and_ there was an empty line (as in the example
given in the reporting issue), we ended up panicking trying to slice an
empty string from 0+1 (== 1).

Let's tighten our check to say that we can't trim when `i` is even the same
as the length of the line, not just when it's greater. (Any such cases
would panic trying to slice `line` from `line.len()+1`.)

Resolves #47197.

Ideally, we should make use of CloudABI's internal proc_raise(SIGABRT)
system call. POSIX abort() requires things like flushing of stdios,
which may not be what we want under panic conditions. Invoking the raw
CloudABI system call would have prevented that.

Unfortunately, we have to make use of the "cloudabi" crate to invoke raw
CloudABI system calls. This is undesired, as discussed in the pull
request (#47190).

This showed up on the Windows bot for testing this PR, and this pr allows
`mark_incr_comp_session_as_invalid` ok if it's already invalid, hopefully
avoiding scary ICEs and instead leaving the nicely printed errors

This is only applicable when neither of --emit=llvm-ir or --emit=llvm-bc are not
requested.

In case either of these outputs are wanted, but the benefits of such context are
desired as well, -Zfewer_names option provides the same functionality regardless
of the outputs requested.

I forgot to update the bootstrap compiler for the 1.23.0 release so let's make
sure it doesn't happen again!

CloudABI uses LLVM's libunwind for stack unwinding. There was a small
bug that went by unnoticed, namely that it was not built with -fno-rtti.
This caused it to (indirectly) depend on the entire C++ runtime.

Now that that issue has been resolved, it is also perfectly fine to make
use of this library for programming languages other than C++.

These no longer work now that Cargo changes the cwd of rustc while it's running.
Instead use an absolute path that's set by rustbuild.

* Bump the release version to 1.25
* Bump the bootstrap compiler to the recent beta
* Allow using unstable rustdoc features on beta - this fix has been applied to
  the beta branch but needed to go to the master branch as well.

The example with the ? operator was missing file.write_all

This mirrors what we for stabilizing the incr. comp. cache and is
necessary for reproducible builds.

Refs #46437

The function was added as a wrapper to handle compatibility with older
LLVM versions that we no longer support, so it can be removed.

Refs #46437