Calls to __rust_probestack

[KyleSiefring]

For security reasons, large stack allocation result in some computations being done.
Thomas thought this was a bug on linux, but is doesn't seem to be. See rust discussion in rust-lang/rust#74405. See a previous commit solving this issue for interprediction: https://github.com/xiph/rav1e/pull/2429/files

These stack allocations occur in many places in the code. The ones that I can think of that I think are large enough to trigger probestack.

• There are a set of arrays in encode_tx_block.

  rav1e/src/encoder.rs

  Lines 1184 to 1197 in d5df5b7

  	let mut residual_storage: Aligned<[i16; 64 * 64]> = Aligned::uninitialized();
  	let mut coeffs_storage: Aligned<[T::Coeff; 64 * 64]> =
  	Aligned::uninitialized();
  	let mut qcoeffs_storage: Aligned<[MaybeUninit<T::Coeff>; 32 * 32]> =
  	Aligned::uninitialized();
  	let mut rcoeffs_storage: Aligned<[T::Coeff; 32 * 32]> =
  	Aligned::uninitialized();
  	let residual = &mut residual_storage.data[..tx_size.area()];
  	let coeffs = &mut coeffs_storage.data[..tx_size.area()];
  	let qcoeffs = init_slice_repeat_mut(
  	&mut qcoeffs_storage.data[..coded_tx_area],
  	T::Coeff::cast_from(0),
  	);
  	let rcoeffs = &mut rcoeffs_storage.data[..coded_tx_area];

• https://github.com/xiph/rav1e/blob/master/src/asm/x86/transform/forward.rs#L348

• rav1e/src/asm/shared/transform/inverse.rs

  Line 30 in c6a2d69

  let mut copied: Aligned<[T::Coeff; 32 * 32]> = Aligned::uninitialized();

The first seems easiest to solve. The changes in this patch can be used as a template: https://github.com/xiph/rav1e/pull/2429/files