If no archive library was found, return from the "plugins" directory
without creating "libarchive_plugins.a".  Empty static libraries are
unsupported on some operating systems such as macOS.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1650

Commit 44ef34db was broken.

Punycode hooray!

It is not explicitly documented whether snd_pcm_name() is allowed to
return NULL:
https://www.alsa-project.org/alsa-doc/alsa-lib/group___p_c_m.html#ga5031edc0422df8db1f70af056a12dd77

But apparently this is legal:
https://github.com/alsa-project/alsa-lib/blob/0222f45d11e8b71bf651b985b00fdb0addbf3eed/src/pcm/pcm.c#L2761-L2762

That's ... surprising!

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1645

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1644

This appears to have been fixed in some recent CURL version.

According to the latest WebDAV specification (RFC4918),
timestamp string in the getlastmodified property is formatted
as rfc1123-date, such as "Sun, 06 Nov 1994 08:49:37 GMT".
However, to process responses from servers in the older style
format specified in RFC2518, timestamps in the HTTP-date format
had better be accepted.

As described in the libcurl api documentation, curl_getdate() can handle
timestamp strings in HTTP-date formats, including rfc1123-date.

https://www.rfc-editor.org/rfc/rfc4918#section-15.7
https://www.rfc-editor.org/rfc/rfc2518.html#section-13.7
https://curl.se/libcurl/c/curl_getdate.html

Fixes compiler warning because formatting unscoped enums is deprecated
since libfmt 9.

This fixes #1616

This fixes a bug introduced in 87fa6bca where the FLAC encoder fails to
initialize unless libFLAC is built with Ogg support. When libFLAC is
built without Ogg support, FLAC__stream_encoder_set_ogg_serial_number
unconditionally returns false.

Don't require "log_file" setting, for "--no-config" operation.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1600