Add support for WASM backend #3312

Job	Run time
nix-build	17m 19s
unit-tests	47s
cabal	8m 6s
runghc	1m 6s
shellFor-not-depends	1m 16s
docs	37m 21s
shellFor-hoogle	1m 21s
hydra-ifdLevel-3	30m 18s
shellFor-multiple-package	30s
maintainer-scripts	49s
tests-benchmarks	7m 51s
hix	57s
hydra-ifdLevel-2	20m 19s
closure-size	8s
plan-extra-hackages	11s
hydra-ifdLevel-0-and-1	5m 44s
multi-target	47s
haskell-nix-roots-do-not-require-IFDs	22s
check-materialization-concurrency	24s
cabal-doExactConfig	18s
shellFor-single-package	28s
build-extra-hackages	13s
update-docs	11s
check-path-support	14s
hydra-without-remote-builders-ghc9102	49m 45s
check-nix-tools	22s
hydra-without-remote-builders-ghc967	4m 32s
hix-cabal	11m 21s
	3h 23m 0s

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