[LIT][LLVM-STRINGS]Make stdin tests shell-consistent (#176139)

The fix updates the llvm-strings stdin lit tests to use `printf` instead
of `echo -n` when generating input via stdin.
The behavior of `echo -n` is not portable and varies across shells and
platforms, particularly on AIX where `/bin/sh` handles `-n` and escape
processing differently from GNU-compatible shells. This causes the tests
to fail despite correct llvm-strings functionality.

In contrast, `printf` has well-defined, POSIX-specified semantics and
provides consistent handling of newlines, escape sequences, and
non-printable characters. Using `printf` eliminates the dependency on
shell-specific `echo` behavior and makes the tests deterministic.
1 file changed
tree: 6727ba39a7ae3f84bf51e1730d8af5cea4f780e7
  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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