Fix help formatting for string and filename options

I happened to notice that "help add-inferior" said:

  -execFILENAME
    FILENAME is the file name of the executable to use as the
    main program.

This is missing a space after "-exec".  This patch fixes the bug.

If ok'd on time I plan to check this in to the gdb-16 branch as well.

Approved-by: Kevin Buettner <kevinb@redhat.com>

(cherry picked from commit 6511d20c9d)

gdb/cli/cli-option.c

@@ -790,10 +790,10 @@ append_val_type_str (std::string &help, const option_def &opt,
       }
       break;
     case var_string:
-      help += "STRING";
+      help += " STRING";
       break;
     case var_filename:
-      help += "FILENAME";
+      help += " FILENAME";
       break;
     default:
       break;

gdb/testsuite/gdb.base/options.exp

@@ -1162,3 +1162,9 @@ test-thread-apply
 
 # Basic "info threads" integration tests.
 test-info-threads
+
+# There was a bug where the "metasyntactic variable" was glued to the
+# option.
+gdb_test "help maintenance test-options unknown-is-operand" \
+    "-string STRING.*-filename FILENAME.*" \
+    "option help has spaces"