gdb: add lookup_cmd_exact to simplify a common pattern

In code dealing with commands, there's a pattern repeated a few times of
calling lookup_cmd with some speficic arguments and then using strcmp
on the returned command to check for an exact match.
As a later patch would add a few more similar lines of code, this patch
adds a new lookup_cmd_exact function which simplify this use case.

gdb/ChangeLog:

	* cli/cli-decode.c (lookup_cmd_exact): Add.
	* cli/cli-script.c (do_define_command): Use lookup_cmd_exact.
	(define_prefix_command): Ditto.
	* command.h: Add lookup_cmd_exact.

1 files changed, 15 insertions, 0 deletions

diff --git a/gdb/cli/cli-decode.c b/gdb/cli/cli-decode.c
index 99bd4c6..f48a9ad 100644
--- a/gdb/cli/cli-decode.c
+++ b/gdb/cli/cli-decode.c
@@ -1875,6 +1875,21 @@ lookup_cmd (const char **line, struct cmd_list_element *list,
   return 0;
 }
 
+/* See command.h.  */
+
+struct cmd_list_element *
+lookup_cmd_exact (const char *name,
+		  struct cmd_list_element *list,
+		  bool ignore_help_classes)
+{
+  const char *tem = name;
+  struct cmd_list_element *cmd = lookup_cmd (&tem, list, "", NULL, -1,
+					     ignore_help_classes);
+  if (cmd != nullptr && strcmp (name, cmd->name) != 0)
+    cmd = nullptr;
+  return cmd;
+}
+
 /* We are here presumably because an alias or command in TEXT is
    deprecated and a warning message should be generated.  This
    function decodes TEXT and potentially generates a warning message