The `req_interp` test attribute is broken for --test-compiler=stage1

Summary

Running hadrian/build --flavour=devel2+debug_ghc+debug_info -j6 test --test-compiler=stage1 --docs=none I get a very large amount of test failures related to missing external interpreter/missing interpreter.

Would be convenient if that would respect the req_interp flag and not try to run all those tests.

Environment

GHC version used: any

Optional:

Operating System: linux
System Architecture: x86

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