Closes https://github.com/MusicPlayerDaemon/MPD/issues/974

cue_next_word() can return a pointer one past the end of the string if
the word is followed by the terminating null byte.

This commit adds some basic infrastructure for fuzzers, and adds a
fuzzer for the CUE sheet parser.

This allows canceling the blocking method LockWaitWriteAvailable(),
and thus allows breaking free of misbehaving ALSA drivers, avoiding a
MPD lockup.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/966

This allows interrupting the output thread (for some plugins which
implement this method).  This way, operations can be canceled
properly, instead of waiting for some external entity.

Move the InternalPlay() call and the wake_cond.wait() call into the
`case Command::NONE` and revert all `continue` statements to a simple
`break`.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/960

clocale is part of C++11.

In practical terms, gcc's libstdc++ comes with its own locale defines
when the libc does not have them.

Also reworked to be dependent on !ANDROID.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with performance-move-const-arg
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with modernize-use-auto
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Fixes use-after-free because the temporary goes out of scope.

We don't support GCC 7 anymore.

Ugly workaround for https://github.com/mesonbuild/meson/issues/1550

"DEFAULT" is a bad name - all it says is that it's the default value,
but it doesn't say what it means.  The name NOTICE mimics the syslog
level.

Calling this "secure" never made sense.  Messages about client
connects are just a small part of what gets logged as "secure",
a.k.a. "info".

Closes https://github.com/MusicPlayerDaemon/MPD/issues/892

My concept with `class CancellableOperation` doesn't work properly,
because the kernel may continue to write to the given buffer as soon
as the read finishes.

To fix this, this commit adds `class ReadOperation` which owns the
buffer and the `struct iovec`.  Instances of this class persist until
the read really finishes, even if the operation is canceled.

And un-deprecate "pause" without parameter (toggles pause).  I have no
idea why it was deprecated long ago; the deprecation notice was copied
from the ancient MPD wiki.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/944

release v0.21.26