Steps to reproduce on a Mac:

$ ./hadrian/build.sh -c -j "binary-dist"
<snip>
Error when running Shake build system:
  at src/Main.hs:58:30-42:
* Depends on: binary-dist
* Raised the exception:
user error (Development.Shake.cmd, system command failed
Command: cp -r _D5316/stage1/lib/x86_64-darwin-ghc-8.7.20181119/rts-1.0/include _D5316/bindist/ghc-8.7.20181119-x86_64-apple-darwin
Exit code: 1
Stderr:
cp: _D5316/stage1/lib/x86_64-darwin-ghc-8.7.20181119/rts-1.0/include: No such file or directory
)

There is an _D5316/stage1/lib/x86_64-osx-ghc-8.7.20181119/rts-1.0/include folder though (note the darwin/osx difference)...

At a glance, I think this is a case of Cabal having a different naming convention then Hadrian's HostOs (I'm pretty sure that the folders in lib are created by Cabal using its internal convention).