Add support for WASM backend #3313

Job	Run time
unit-tests	2m 57s
cabal	1m 19s
runghc	12m 0s
nix-build	9m 45s
check-path-support	1m 13s
hydra-ifdLevel-3	30m 17s
docs	12m 44s
maintainer-scripts	11s
hydra-ifdLevel-0-and-1	20m 18s
update-docs	56s
cabal-doExactConfig	11s
closure-size	28s
check-materialization-concurrency	23s
shellFor-hoogle	11s
shellFor-not-depends	1m 14s
tests-benchmarks	13s
shellFor-multiple-package	11s
multi-target	13s
hydra-ifdLevel-2	20m 18s
plan-extra-hackages	14s
build-extra-hackages	7m 33s
shellFor-single-package	11s
check-nix-tools	1m 9s
hydra-without-remote-builders-ghc967	1m 27s
hix	1m 33s
hydra-without-remote-builders-ghc9102	46s
haskell-nix-roots-do-not-require-IFDs	11s
hix-cabal	24s
	2h 8m 30s

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