dd: fix ISO-8859-1 case conversion for conv=lcase/ucase

[sylvestre]

No description provided.

[collinfunk]

This assumes that the user is using a ISO-8859-1 locale and not another unibyte locale, e.g., ISO-8859-9.

[ChrisDryden]

I think we're going to have to build the runtime conversion to use libc to get the locale data for these

  pub fn build_lcase_table() -> ConversionTable {
      let mut table = [0u8; 256];
      for i in 0..256 {
          table[i] = unsafe { libc::tolower(i as libc::c_int) } as u8;
      }
      table
  }

  pub fn build_ucase_table() -> ConversionTable {
      let mut table = [0u8; 256];
      for i in 0..256 {
          table[i] = unsafe { libc::toupper(i as libc::c_int) } as u8;
      }
      table
  }

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail/retry. tests/tail/retry is passing on 'main'. Maybe you have to rebase?
Congrats! The gnu test tests/dd/conv-case is no longer failing!
Congrats! The gnu test tests/tail/tail-n0f is now passing!

[sylvestre]

testing a different approach

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/dd/conv-case is no longer failing!
Congrats! The gnu test tests/tail/tail-n0f is now passing!