Add support for WASM backend #3080

Job	Run time
cabal	17s
cabal-doExactConfig	12s
multi-target	43s
nix-build	1h 25m 39s
runghc	12s
shellFor-hoogle	22s
shellFor-multiple-package	29s
shellFor-single-package	37s
tests-benchmarks	12s
build-extra-hackages	26s
hix	1m 2s
unit-tests	6s
maintainer-scripts	10s
plan-extra-hackages	8s
shellFor-not-depends	26s
check-materialization-concurrency	22s
check-path-support	7s
docs	57s
closure-size	5s
haskell-nix-roots-do-not-require-IFDs	12s
hydra-ifdLevel-0-and-1	12s
hydra-ifdLevel-2	10s
hydra-ifdLevel-3	13s
hydra-without-remote-builders-ghc967	1m 29s
update-docs	5s
hix-cabal	8s
hydra-without-remote-builders-ghc9102	2m 31s
nix-tools	23s
	1h 37m 55s

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