Motivation for this change

Spotted while updating, although it looks familiar...
(was this fixed in llvm8 expression but not here, maybe?)

Anyway, I'm not sure immediately how to best test this--
since builds like
pkgsCross.aarch64-multiplatform.llvmPackages_7.compiler-rt
encounter errors in the build before getting to this part...

(it probably is best-tested with llvm-based toolchains, yes? :))

Ah, here it is:

d453273

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.