Some FFmpeg filters change the sample format, and since MPD assumes
this never happens, this results in loud noise instead of music.  This
commit finally implements the TODO comment by sending one frame of
silence to the filter and checking the output frame's format.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1009

To be reused by the FFmpeg filter plugin.

This compatibility macro has been removed from FFmpeg long ago.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/981

Reduces header dependencies.

snprintf() is available on mingw, and the libnfs kludge broke the
build with mingw, because sprintf_s() was now both an inline function
and a "dllimport" function (because the macro renamed the inline
function snprintf() to sprintf_s() in mingw's stdio.h).

GCC5 cannot build mpd.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Need to check for it in iconv.h. Otherwise meson prefixes a __builtin variant in the check.

Preparing to replace `smbclient_mutex`, for finer-grained locking.

We no longer need to call smbc_init() because we don't need the compat
layer anymore.

As a side effect, the input plugin closes the SMB/CIFS connection
after closing the file.

This solves one part of
https://github.com/MusicPlayerDaemon/MPD/issues/916

Prepare for templated functions.

Our Windows build is built with `--disable-netrc`, and that makes
CURLOPT_NETRC fail, causing failures with all streams.  D'oh!

Closes https://github.com/MusicPlayerDaemon/MPD/issues/886

The ones in std have overloads for const char/char.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Passing `length+1` to `MultiByteToWideChar()` means the function may
fill the whole buffer with output data, and could theoretically
overwrite the null terminator.  In practice, this will never happen,
but this way, it's slightly more correct.

Also, null-terminate after `MultiByteToWideChar()`, after we got the
real output length.  Again, this would never have been a problem, but
who knows...

libavutil's macro definition is a compound literal, which is illegal
in C++.  Fixes yet another -Wpedantic warning.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

This makes ccache more efficient when recompiling with different
plugins.