Reland "[Clang][CodeGen] Report when an alias points to an incompatible target" (#195550)

This relands #192397, which was reverted in #194106. The new version
includes the following fixes:
- Set an explicit triple in the `attr-alias.m` test because aliases are
not supported on Darwin.
- Relax the check to only diagnose mismatches in return types and
parameter lists, while ignoring exception specifications and other
attributes.

Original description follows:

Add checks to ensure that an alias and its target have compatible types:
- Generate an error if a function alias points to a variable or vice
versa.
- Issue a warning for mismatches in function types.
- Ignore type discrepancies for variables.

This behavior aligns with similar diagnostics in GCC.

Resolves: #47301
8 files changed
tree: d8e0163b991b23ee6cac556d0b2695a46edf5722
  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. libsycl/
  16. libunwind/
  17. lld/
  18. lldb/
  19. llvm/
  20. llvm-libgcc/
  21. mlir/
  22. offload/
  23. openmp/
  24. orc-rt/
  25. polly/
  26. runtimes/
  27. third-party/
  28. utils/
  29. .clang-format
  30. .clang-format-ignore
  31. .clang-tidy
  32. .git-blame-ignore-revs
  33. .gitattributes
  34. .gitignore
  35. .mailmap
  36. CODE_OF_CONDUCT.md
  37. CONTRIBUTING.md
  38. LICENSE.TXT
  39. pyproject.toml
  40. README.md
  41. SECURITY.md
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