* event-top.c (cli_command_loop): Replace readline setup with
direct call to display_gdb_prompt.
(display_gdb_prompt): Do not call observer mechanism during
synchronous execution.
testsuite:
* lib/prompt.exp: New file for testing the first prompt.
* gdb.python/py-prompt.exp: Ditto.
* gdb.python/py-prompt.c: Ditto (copy of ext-attach.c).