Add support for WASM backend #3316

Job	Run time
nix-build	2m 58s
unit-tests	23s
cabal	6h 0m 16s
update-docs	18s
hydra-ifdLevel-2	20m 18s
runghc	6h 0m 20s
cabal-doExactConfig	30s
tests-benchmarks	21s
build-extra-hackages	6h 0m 16s
hydra-ifdLevel-3	30m 17s
shellFor-not-depends	15s
hix	36m 29s
maintainer-scripts	11s
hydra-ifdLevel-0-and-1	4m 5s
multi-target	13s
check-materialization-concurrency	23s
closure-size	9s
shellFor-hoogle	6h 0m 17s
docs	6h 0m 17s
plan-extra-hackages	11s
shellFor-multiple-package	6h 0m 17s
shellFor-single-package	6h 0m 17s
check-path-support	6h 0m 16s
haskell-nix-roots-do-not-require-IFDs	6h 0m 17s
hydra-without-remote-builders-ghc967	1m 19s
hydra-without-remote-builders-ghc9102	1m 10s
check-nix-tools	2h 51m 58s
hix-cabal	6h 0m 17s
	2d 16h 34m 18s

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