[flang][nfc] Add missing build dependency

[flang][nfc] Add missing build dependency

Two buildbots have started failing recently:
* https://lab.llvm.org/buildbot/#/builders/181/builds/3894
* https://lab.llvm.org/buildbot/#/builders/191/builds/3908

Build error:
```
In file included from /home/tcwg-buildbot/worker/flang-aarch64-rel-assert/llvm-project/flang/examples/FlangOmpReport/FlangOmpReport.cpp:21:
In file included from /home/tcwg-buildbot/worker/flang-aarch64-rel-assert/llvm-project/flang/include/flang/Frontend/FrontendActions.h:15:
In file included from /home/tcwg-buildbot/worker/flang-aarch64-rel-assert/llvm-project/llvm/../mlir/include/mlir/IR/BuiltinOps.h:16:
In file included from /home/tcwg-buildbot/worker/flang-aarch64-rel-assert/llvm-project/llvm/../mlir/include/mlir/IR/FunctionInterfaces.h:17:
In file included from /home/tcwg-buildbot/worker/flang-aarch64-rel-assert/llvm-project/llvm/../mlir/include/mlir/IR/BuiltinTypes.h:12:
/home/tcwg-buildbot/worker/flang-aarch64-rel-assert/llvm-project/llvm/../mlir/include/mlir/IR/BuiltinAttributeInterfaces.h:279:10: fatal error: 'mlir/IR/BuiltinAttributeInterfaces.h.inc' file not found
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
```

I have not been able to reproduce locally, but from this log it is clear
that the rule for `flangFrontend` is missing the
`MLIRBuiltinAttributeInterfacesIncGen` dependency from MLIR.  I couldn't
identify a breaking commit. I suspect that until now we have simply been
"lucky" and that dependency just happened to be built before
`flangFrontend`.

I am sending this without a review - the change is rather
straightforward and the only way to verify it is to make the buildbots
test it.