Add support for WASM backend #3344

Job	Run time
unit-tests	12s
cabal-doExactConfig	6m 18s
maintainer-scripts	11s
nix-build	1m 42s
shellFor-hoogle	9m 15s
multi-target	40s
runghc	15s
cabal	17s
shellFor-multiple-package	9m 25s
tests-benchmarks	1m 50s
shellFor-single-package	25s
shellFor-not-depends	27s
hydra-ifdLevel-2	5m 53s
hydra-without-remote-builders-ghc967	5m 15s
hydra-ifdLevel-3	30m 17s
check-nix-tools	4m 54s
hydra-without-remote-builders-ghc9102	6m 51s
hydra-ifdLevel-0-and-1	4m 20s
update-docs	9s
docs	1m 34s
check-materialization-concurrency	23s
plan-extra-hackages	14s
hix-cabal	13s
haskell-nix-roots-do-not-require-IFDs	27s
closure-size	9s
build-extra-hackages	14s
hix	5m 31s
check-path-support	19s
	1h 37m 40s

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