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.

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

Use a boolean flag instead.

Avoid NaN to allow -ffast-math.

Avoid NaN to allow -ffast-math.

Don't require a writable string, and don't modify it.

Prepare to migrate away from GLib.  Currently, we're still using GLib
as a backend.

Fixes build problems with mingw32.

Not a CPP macro.  This adds the "unused" attribute to "saveptr", which
eliminates one gcc warning.

Remove cross_fade_apply(), and call pcm_mix() in the output thread,
mixing the chunk and chunk->other together.

Adds mixrampdb and mixrampdelay commands.  Reads MIXRAP_START and
MIXRAMP_END tags from FLAC files and overlaps instead of crossfading.

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.