Add support for WASM backend #3332

Job	Run time
unit-tests	31s
nix-build	12m 34s
runghc	27m 10s
tests-benchmarks	27m 11s
cabal	1m 21s
cabal-doExactConfig	14s
shellFor-single-package	28m 43s
shellFor-not-depends	30s
plan-extra-hackages	11s
maintainer-scripts	11s
shellFor-hoogle	9m 42s
multi-target	1m 13s
shellFor-multiple-package	2m 18s
build-extra-hackages	16s
closure-size	7s
update-docs	10s
docs	22m 26s
hix-cabal	8m 7s
check-path-support	34s
haskell-nix-roots-do-not-require-IFDs	32s
check-materialization-concurrency	25s
hydra-without-remote-builders-ghc9102	1h 2m 26s
hydra-without-remote-builders-ghc967	1h 0m 1s
hix	47m 16s
check-nix-tools	48s
hydra-ifdLevel-0-and-1	5m 45s
hydra-ifdLevel-2	20m 17s
hydra-ifdLevel-3	30m 23s
	6h 11m 22s

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