Some macOS users were experiencing build failures where pkg-config
could not find poppler, even with Homebrew's poppler package installed.
This occurs when Homebrew doesn't properly link the .pc files to the
standard pkg-config search path.

Fixes #299

Alpine Linux deprecated sudo in favor of doas. Add doas support to
exec_privileged() so autobuild works on Alpine without requiring users
to install and configure sudo.

Fixes #323

Notes from the original PR:

The dependencies for android in autobuild can not be installed in
pdf-tools-install, they have to be installed manually in Termux. But
the dependencies are checked when running autobuild.

pdf-tools-install successfully installs epdfinfo in Android Emacs. One
can then view pdf files.

The shebang in autobuild does not work in Termux, I therefore had to
create a separate script "autobuild.android" that in turn executes
autobuild. The problem with the shebang is that "env" in Termux is not
located at "/usr/bin/env".

pdf-tools/Makefile does currently not work in Android Emacs, but it is
not needed for running pdf-tools-install. Fixing this will have to be
done in a separate pull request, if deemed necessary. Reason: There is
yet no consensus for how to implement a command line emacs, to be run
in batch mode, in Android Emacs.

I have successfully run "make test" in Ubuntu, in the repo feature
branch. Running "make server-test" in the master branch fails, so I
have not tested this in the feature branch.

Closes: #230
Author: @johanwiden

Add build support for Nobara Linux, a Fedora derivative.

- Add os_nobara() detection function (checks /etc/nobara-release)
- Uses same packages as Fedora (dnf package manager)
- Add to --os argument handling and auto-detection chain

Closes: #301
Author: @gs-101

Support the newer UCRT64 MSYS2 environment (recommended default per msys2.org).

- Add UCRT64 detection to server/autobuild
- Fix vasprintf implicit declaration error on Windows (synctex_parser.c)
- Update configure.ac for Windows compatibility

Fixes #282, #286
Supersedes #295

Tested by multiple users on Windows 10/11 with MSYS2.

Co-authored-by: legends2k

Copying my comment from the Github issue:

> The problem is that something seems to have changed in the way brew
> installs glib, due to which pkg-config does not find the glib headers.
>
> To fix this, I have updated the autobuild script to manually modify
> the PKG_CONFIG_PATH. This should fix the problem.
>
> I will test the change and close this issue via the commit once I push
> it. You will need to update your version of pdf-tools and then restart
> Emacs to trigger the re-build again. (It might take a few hours for
> Melpa to pick up the latest version of the pdf-tools)
>
> I will create a linked issue to investigate a better long-term
> solution to this problem.

Closes: #269

In Void Linux most heading/development files are separated from the "main" packages and are stored on `${package-name}-devel`. The autobuild for Void fails because it tries to find `cairo-devel`, which contains `cairo`, respectives headers and other dependencies.

This Pull Request adds `cairo-devel` to the `PACKAGES` variable

This commit is a squashed commit of PR #164 by @skyler544

Author: Skyler Mayfield <skyler544@gmail.com>
Date:   Fri Oct 21 12:00:46 2022 +0200
Closes: #164