[CommandLine] Change help output to prefix long options with `--` instead of `-`. NFC . Part 3 of 5

Summary:
By default, `parseCommandLineOptions()` will accept either a
`-` or `--` prefix for long options -- options with names longer than
a single character.

While this change does not affect behavior, it will be helpful with a
subsequent change that requires long options use the `--` prefix.

Reviewers: rnk, thopre

Reviewed By: thopre

Subscribers: thopre, cfe-commits, hiraditya, llvm-commits

Tags: #llvm, #clang

Differential Revision: https://reviews.llvm.org/D61269

llvm-svn: 359909
5 files changed
tree: f82a3799e99dd46b871e4e42f9e526c3108f7332
  1. clang/
  2. clang-tools-extra/
  3. compiler-rt/
  4. debuginfo-tests/
  5. libclc/
  6. libcxx/
  7. libcxxabi/
  8. libunwind/
  9. lld/
  10. lldb/
  11. llgo/
  12. llvm/
  13. openmp/
  14. parallel-libs/
  15. polly/
  16. pstl/
  17. .arcconfig
  18. .clang-format
  19. .clang-tidy
  20. .gitignore
  21. README.md
README.md

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