[19.09] zfs: 0.8.2 -> 0.8.3

[Frostman]

Motivation for this change

Zfs 0.8.3 is included into release-20.03 and it contains many important fixes and improvements https://github.com/zfsonlinux/zfs/releases/tag/zfs-0.8.3 such as - Linux 5.0 compat: SIMD compatibility openzfs/zfs#8965

Additionally, synced two more minor patches to get release-19.09 up to date with master.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

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This change is 

[Frostman]

I've tested it locally with nixpkgs-review and it succeded. The nixosTests.installer.zfsroot passes as well.

[Frostman]

@GrahamcOfBorg build nixosTests.installer.zfsroot

[Mic92]

Actually we should not been affected by the SIMD patch because I simply patched the kernel to expose the fpu functions needed by ZFS. I might have not backported those to stable though.

[Mic92]

However support for new kernels is a good thing to have nevertheless.

[Mic92]

I will merge this together with #80008