Use softfloat abi in the target spec for aarch64

This allows removing the -Csoft-float argument when building.

mentioned in merge request cookbook!392 (merged)

added 5 commits

• 3f32858d...441385dd - 4 commits from branch redox-os:master
• d43eb74d - Use softfloat abi in the target spec for aarch64

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merged

-Csoft-float apparently does nothing on aarch64, so before this change likely the hardfloat ABI was used here.