[SFrames] reland Emit and relax FREs #158154 (#159643)

[Previously reverted due to msan failures on two uninitialized padding
bits.]

This PR emits and relaxes the FREs generated in the previous PR.

After this change llvm emits usable sframe sections that can be linked
with the gnu linker. There are a few remaining cfi directives to handle
before they are generally usable, however.

The output isn't identical with gnu-gas in every case (this code
produces fewer identical FREs in a row than gas), but I'm reasonably
sure that they are correct regardless. There are even more size
optimizations that can be done later.

Also, while working on the tests, I found a few bugs in older portions
and cleaned those up.

This is a fairly big commit, but I'm not sure how to make it smaller.
13 files changed
tree: 7126d64a326a5e105227e1250c0958ff56538de0
  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
README.md

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