Make extract_arg return a std::string

Change extract_arg to return a std::string and fix up all the users.
I think string is mildly better than unique_xmalloc_ptr<char>, when
possible, because it provides a more robust API.

I changed the error messages emitted from find_location_by_number to
avoid either writing to a string or an extra allocation; this can be
changed but I thought that the new message was not any less clear.
You can see an example in the testsuite patch.

ChangeLog
2017-09-11  Tom Tromey  <tom@tromey.com>

	* demangle.c (demangle_command): Update.
	* breakpoint.c (disable_command): Update.
	(enable_command): Update.
	(find_location_by_number): Make "number" const.  Use
	get_number_trailer.
	* cli/cli-utils.c (extract_arg): Return std::string.
	* probe.c (parse_probe_linespec): Update.  Change types.
	(collect_probes): Take string arguments.
	(parse_probe_linespec): Likewise.
	(info_probes_for_ops): Update.
	(enable_probes_command): Update.
	(disable_probes_command): Update.
	* break-catch-sig.c (catch_signal_split_args): Update.
	* mi/mi-parse.c (mi_parse): Update.

testsuite/ChangeLog
2017-09-11  Tom Tromey  <tom@tromey.com>

	* gdb.base/ena-dis-br.exp (test_ena_dis_br): Update test.

1 files changed, 6 insertions, 6 deletions

diff --git a/gdb/break-catch-sig.c b/gdb/break-catch-sig.c
index 805084fda1f..5bc3aed09d7 100644
--- a/gdb/break-catch-sig.c
+++ b/gdb/break-catch-sig.c
@@ -343,12 +343,12 @@ catch_signal_split_args (char *arg, bool *catch_all)
       gdb_signal signal_number;
       char *endptr;
 
-      gdb::unique_xmalloc_ptr<char> one_arg (extract_arg (&arg));
-      if (one_arg == NULL)
+      std::string one_arg = extract_arg (&arg);
+      if (one_arg.empty ())
 	break;
 
       /* Check for the special flag "all".  */
-      if (strcmp (one_arg.get (), "all") == 0)
+      if (one_arg == "all")
 	{
 	  arg = skip_spaces (arg);
 	  if (*arg != '\0' || !first)
@@ -361,14 +361,14 @@ catch_signal_split_args (char *arg, bool *catch_all)
       first = false;
 
       /* Check if the user provided a signal name or a number.  */
-      num = (int) strtol (one_arg.get (), &endptr, 0);
+      num = (int) strtol (one_arg.c_str (), &endptr, 0);
       if (*endptr == '\0')
 	signal_number = gdb_signal_from_command (num);
       else
 	{
-	  signal_number = gdb_signal_from_name (one_arg.get ());
+	  signal_number = gdb_signal_from_name (one_arg.c_str ());
 	  if (signal_number == GDB_SIGNAL_UNKNOWN)
-	    error (_("Unknown signal name '%s'."), one_arg.get ());
+	    error (_("Unknown signal name '%s'."), one_arg.c_str ());
 	}
 
       result.push_back (signal_number);