[clang][scan-deps] Report a scanned TU's visible modules (#147969)

Clients of the dependency scanning service may need to add dependencies
based on the visibility of importing modules, for example, when
determining whether a Swift overlay dependency should be brought in
based on whether there's a corresponding **visible** clang module for
it.
This patch introduces a new field `VisibleModules` that contains all the
visible top-level modules in a given TU.
Because visibility is determined by which headers or (sub)modules were
imported, and not top-level module dependencies, the scanner now
performs a separate DFS starting from what was directly imported for
this computation.

In my local performance testing, there was no observable performance
impact.

resolves: rdar://151416358

---------

Co-authored-by: Jan Svoboda <jan@svoboda.ai>
8 files changed
tree: 3868d4c5d5583edd9f775da11389b686030fe806
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. flang-rt/
  11. libc/
  12. libclc/
  13. libcxx/
  14. libcxxabi/
  15. libunwind/
  16. lld/
  17. lldb/
  18. llvm/
  19. llvm-libgcc/
  20. mlir/
  21. offload/
  22. openmp/
  23. polly/
  24. runtimes/
  25. third-party/
  26. utils/
  27. .clang-format
  28. .clang-format-ignore
  29. .clang-tidy
  30. .git-blame-ignore-revs
  31. .gitattributes
  32. .gitignore
  33. .mailmap
  34. CODE_OF_CONDUCT.md
  35. CONTRIBUTING.md
  36. LICENSE.TXT
  37. pyproject.toml
  38. README.md
  39. SECURITY.md
README.md

The LLVM Compiler Infrastructure

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Welcome to the LLVM project!

This repository contains the source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and run-time environments.

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