PR14396: Add pretty-printing support for UTF

PR14396: Add pretty-printing support for UTF

* dwarf_wrappers.h: Define DW_ATE_UTF if elfutils < 0.155.
* tapsets.cxx (dwarf_pretty_print::recurse_base): Print UTF with %#c
  too. This will generally only work with the ASCII subset for now...
  (dwarf_pretty_print::print_chars): Match strings by char/UTF encoding
  types, rather than by type name, and use the byte_size to select the
  correct string dereferencing function.
* testsuite/systemtap.base/utf_pretty.*: Test it!