Add support for WASM backend #3314

Job	Run time
nix-build	5m 29s
maintainer-scripts	12s
unit-tests	9s
shellFor-not-depends	4m 32s
multi-target	2m 17s
shellFor-hoogle	53m 45s
runghc	41m 58s
shellFor-multiple-package	34m 5s
cabal-doExactConfig	4h 55m 41s
build-extra-hackages	4h 19m 6s
cabal	49m 48s
shellFor-single-package	5h 18m 39s
plan-extra-hackages	14s
tests-benchmarks	4h 12m 56s
haskell-nix-roots-do-not-require-IFDs	24s
hydra-without-remote-builders-ghc9102	34s
hix	53m 15s
hix-cabal	4m 32s
hydra-ifdLevel-0-and-1	3m 31s
check-path-support	12s
hydra-without-remote-builders-ghc967	10s
docs	46s
check-nix-tools	15s
check-materialization-concurrency	24s
hydra-ifdLevel-2	11m 45s
hydra-ifdLevel-3	30m 18s
update-docs	9s
closure-size	8s
	23h 45m 14s

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