The kernel team thinks about switching the Linux kernel over to building
with clang.  For the way this works we really need multi-arch support
for the compiler (and also llvm-* and lld-* packages), aka those packages
needs to be marked as Multi-Arch: foreign, so we always get a usable one.

Currently at least clang-* is not marked this way.  Also it seems this
package is currently used for two purposes:
- Provide the programs.  Those need to be m-a:foreign.
- Provide the dependencies to pull in development stuff for c, c++ and
  so standard libs.  Those need to be m-a:same.

gcc did this by introducing "gcc-for-host" packages, which via
indirection can be used via build-depends.

Bastian