The Swift compiler derivation modifies the clang wrapper to use
`exec -a "$0"` to allow it to use the same binary for both `clang` and
`clang++`. The sed script it uses to do this fails after the cc-wrapper
changes in 6f2b3ba027 were merged.
This is fixed by updating `makeClangWrapper` to work with the cc-wrapper
changes by having Bash invoke a simple script that uses `exec -a "$0"`
to set the required name for clang.
This fixes the staging-next build failures with Swift on Darwin and Linux.
https://github.com/NixOS/nixpkgs/pull/248496#issuecomment-1676831102
e7cf9a7c45