Add support for WASM backend #3216

Job	Run time
nix-build	4m 5s
runghc	1m 19s
cabal	1m 1s
unit-tests	10s
shellFor-single-package	1m 35s
shellFor-hoogle	1m 7s
shellFor-not-depends	1m 15s
multi-target	2m 33s
hydra-ifdLevel-0-and-1	5m 43s
closure-size	7s
check-nix-tools	16s
cabal-doExactConfig	13s
check-path-support	21s
plan-extra-hackages	14s
check-materialization-concurrency	24s
hydra-without-remote-builders-ghc967	3m 57s
build-extra-hackages	15s
shellFor-multiple-package	18s
update-docs	8s
docs	3m 38s
haskell-nix-roots-do-not-require-IFDs	38s
hix	34s
hydra-ifdLevel-3	30m 18s
maintainer-scripts	10s
tests-benchmarks	15s
hydra-ifdLevel-2	9m 19s
hix-cabal	19s
hydra-without-remote-builders-ghc9102	2m 57s
	1h 13m 9s

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