This is the case with uClibc-ng currently.
Signed-off-by: Rosen Penev <rosenp@gmail.com>
(cherry picked from commit 769cd0ee9f0cf8ceb026aa751b5d4a390bb5dbdc)
(changed define to match master)

It appears that [[fallthrough]] is valid in C++ but not in C. And
in some Clang versions (e.g. Clang 11 on macOS), Clang is pedantic
about this and considers it an error to use [[fallthrough]] in a
.c file such as src/util/format.c.

This changes makes gcc_fallthrough a no-op under Clang in C files.

Older clang versions don't support the GCC __attribute__ syntax.  For
those, don't use anything at all, and new clang versions shall use the
standard syntax.

Works around build failures with ccache which may feed processed code
to GCC, which doesn't have the "fall through" code comments.

Instead of passing tag and group, pass an array of tags.  To support a
nested return value, return a nested std::map of std::maps.  Each key
specifies the tag value, and each value may be another nesting level.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/408

Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

So long, autotools!  This is my last MPD related project to migrate
away from it.  It has its strengths, but also very obvious weaknesses
and weirdnesses.  Today, many of its quirks are not needed anymore,
and are cumbersome and slow.  Now welcome our new Meson overlords!