Use SZFMT for printing size_t
Initialize a couple variables mingw complains about
Update cross-compiler toolchain to work better with Qt
Fix 5.1 surround sound

Apparently, 5.1 surround sound is supposed to use the "side" channels, not the
back channels, and we've been wrong this whole time. That means the "5.1 Side"
is actually the correct 5.1 setup, and using the back channels is anomalous.

Additionally, this means the 5.1 buffer format should also use the the side
channels instead of the back channels.

A final note: the 5.1 mixing coefficients are changed so both use the original
5.1 surround sound set (with the surround channels at +/-110 degrees). So the
only difference now between 5.1 "side" and 5.1 "back" is the channel labels.
Use shorter display names for the surround sound config options
Use a separate macro for the max output channel count
Rename speakers to channels, and remove an old incorrect comment
Pas the output device channel count to ALeffectState::process
Fallback to 16-bit samples in alffmpeg if a float32 format isn't supported
Move a declaration
Rename a couple parameters
Go to the next voice when a source is stopped
Only enable the BS2B filter with stereo output
Add a workaround for compilers without __COUNTER__

This can make GCC pretty noisey, complaining "declaration does not declare
anything" for each static_assert, but it should still function on such older
compilers.
Merge remote-tracking branch 'upstream/master'