maint: adjust quoting: emit '...', not `...' in diagnostics

maint: adjust quoting: emit '...', not `...' in diagnostics

* src/csplit.c (parse_repeat_count, extract_regexp): As above.
* src/date.c (main): Likewise.
* src/ls.c (decode_switches): Likewise.
* src/od.c (decode_one_format, main): Likewise.
* src/pathchk.c (no_leading_hyphen): Likewise.
* src/pr.c (main, getoptarg): Likewise.
* src/rm.c (diagnose_leading_hyphen): Likewise.
* src/sort.c (key_warnings, incompatible_options, main): Likewise.
* src/stat.c (print_esc_char): Print '\x', not `\x' in diagnostic.
* src/test.c (main): Likewise.
* src/touch.c (main): Likewise.
* src/tr.c (build_spec_list, validate, append_range): Likewise.
* tests/misc/mktemp: This is an unusual case, since the affected
string contains only the ` of an `...' string.  So we change
the long ` to a lone '.
* tests/pr/pr-tests: Manual quote adapting fix-up.
* tests/ln/hard-to-sym: Likewise.
* tests/split/suffix-length: Likewise.
* tests/mv/part-fail: Likewise.
* tests/misc/chcon: Likewise.
* tests/misc/stat-printf: Likewise.