Add support for WASM backend #3070

Job	Run time
cabal	32s
cabal-doExactConfig	31s
build-extra-hackages	28s
check-materialization-concurrency	20s
check-path-support	25s
closure-size	4s
docs	1m 59s
haskell-nix-roots-do-not-require-IFDs	1m 46s
hix	42s
hix-cabal	1m 59s
hydra-ifdLevel-0-and-1	5m 56s
hydra-ifdLevel-2	14m 57s
hydra-ifdLevel-3	30m 11s
hydra-without-remote-builders-ghc9101	5m 55s
hydra-without-remote-builders-ghc967	2m 3s
maintainer-scripts	25s
multi-target	33s
nix-build	1m 24s
nix-tools	19s
plan-extra-hackages	6s
runghc	11s
shellFor-hoogle	17s
shellFor-multiple-package	25s
shellFor-not-depends	28s
shellFor-single-package	27s
tests-benchmarks	11s
unit-tests	6s
update-docs	6s
	1h 12m 46s

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