Add better support for armv7a cross compilation #2820

Job	Run time
build-extra-hackages	7s
cabal-doExactConfig	13s
cabal	9s
check-materialization-concurrency	19s
check-path-support	5s
closure-size	4s
docs	18s
haskell-nix-roots-do-not-require-IFDs	12s
hix	43s
hix-cabal	4m 44s
hydra-ifdLevel-0-and-1	7m 11s
hydra-ifdLevel-2	3m 56s
hydra-ifdLevel-3	3m 29s
hydra-without-remote-builders-ghc8107	15s
hydra-without-remote-builders-ghc9101	7s
maintainer-scripts	7s
multi-target	31s
nix-build	26s
nix-tools	15s
plan-extra-hackages	7s
runghc	11s
shellFor-hoogle	8s
shellFor-multiple-package	14s
shellFor-not-depends	12s
tests-benchmarks	7s
shellFor-single-package	16s
unit-tests	4s
update-docs	5s
	24m 35s

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