[gdb/testsuite] Reimplement gdb.gdb/complaints.exp as unittest

When building gdb with "-Wall -O2 -g -flto=auto", I run into:
...
(gdb) call clear_complaints()^M
No symbol "clear_complaints" in current context.^M
(gdb) FAIL: gdb.gdb/complaints.exp: clear complaints
...

The problem is that lto has optimized away the clear_complaints function
and consequently the selftest doesn't work.

Fix this by reimplementing the selftest as a unit test.

Factor out two new functions:
- void
  execute_fn_to_ui_file (struct ui_file *file, std::function<void(void)> fn);
- std::string
  execute_fn_to_string (std::function<void(void)> fn, bool term_out);
and use the latter to capture the complaints output.

Tested on x86_64-linux.

1 files changed, 19 insertions, 7 deletions

diff --git a/gdb/gdbcmd.h b/gdb/gdbcmd.h
index f541ebd..27550c1 100644
--- a/gdb/gdbcmd.h
+++ b/gdb/gdbcmd.h
@@ -134,17 +134,29 @@ extern struct cmd_list_element *save_cmdlist;
 
 extern void execute_command (const char *, int);
 
-/* Run execute_command for P and FROM_TTY.  Capture its output into the
-   returned string, do not display it to the screen.  The global BATCH_FLAG
-   will temporarily be set to true.  When TERM_OUT is true the output is
-   collected with terminal behaviour (e.g. with styling).  When TERM_OUT is
-   false raw output will be collected (e.g. no styling).  */
+/* Run FN.  Sends its output to FILE, do not display it to the screen.
+   The global BATCH_FLAG will be temporarily set to true.  */
+
+extern void execute_fn_to_ui_file (struct ui_file *file, std::function<void(void)> fn);
+
+/* Run FN.  Capture its output into the returned string, do not display it
+   to the screen.  The global BATCH_FLAG will temporarily be set to true.
+   When TERM_OUT is true the output is collected with terminal behaviour
+   (e.g. with styling).  When TERM_OUT is false raw output will be collected
+   (e.g. no styling).  */
+
+extern std::string execute_fn_to_string (std::function<void(void)> fn, bool term_out);
+
+/* As execute_fn_to_ui_file, but run execute_command for P and FROM_TTY.  */
 
-extern std::string execute_command_to_string (const char *p, int from_tty,
-					      bool term_out);
 extern void execute_command_to_ui_file (struct ui_file *file,
 					const char *p, int from_tty);
 
+/* As execute_fn_to_string, but run execute_command for P and FROM_TTY.  */
+
+extern std::string execute_command_to_string (const char *p, int from_tty,
+					      bool term_out);
+
 extern void print_command_line (struct command_line *, unsigned int,
 				struct ui_file *);
 extern void print_command_lines (struct ui_out *,