stdenv: partial revert of f2bb59

/cc @Ericson2314

This line broke MacOS cross compilation. paxctl cannot be built on
macOS. Maybe it can be fixed, but no reason to break things
unnecessarily.

Regardless, you definitely need to be more careful about backporting.
I think it’s fine to move fast and break things on master but
with release-18.09 we should be more careful. Something like more
automated testing for cross compilation would also be
helpful (hopefully even making it block).