fixup! fixup! Add --drop-unused-functions option

Author: tautschnig

src/goto-instrument/goto_instrument_parse_options.cpp

@@ -1482,6 +1482,7 @@ void goto_instrument_parse_optionst::help()
     " --show-symbol-table          show symbol table\n"
     " --list-symbols               list symbols with type information\n"
     HELP_SHOW_GOTO_FUNCTIONS
+    " --drop-unused-functions      drop functions trivially unreachable from main function\n" // NOLINT(*)
     " --print-internal-representation\n" // NOLINTNEXTLINE(*)
     "                              show verbose internal representation of the program\n"
     " --list-undefined-functions   list functions without body\n"