Add support for WASM backend #3349

Job	Run time
cabal	1m 18s
unit-tests	9s
nix-build	22m 58s
shellFor-hoogle	4m 32s
build-extra-hackages	35s
tests-benchmarks	45s
runghc	2m 48s
multi-target	4m 38s
shellFor-single-package	5m 8s
shellFor-not-depends	42s
shellFor-multiple-package	4m 0s
plan-extra-hackages	14s
cabal-doExactConfig	1m 6s
maintainer-scripts	9s
check-materialization-concurrency	25s
check-path-support	21s
hydra-without-remote-builders-ghc967	6m 18s
closure-size	8s
hydra-without-remote-builders-ghc9102	6m 48s
haskell-nix-roots-do-not-require-IFDs	20s
docs	1h 24m 48s
check-nix-tools	16s
hix-cabal	36s
hix	46s
hydra-ifdLevel-0-and-1	5m 30s
hydra-ifdLevel-2	20m 19s
update-docs	9s
hydra-ifdLevel-3	30m 18s
	3h 26m 4s

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