pythongh-110166: Fix gdb CFunctionFullTests on ppc64le clang build (python#110331)

CFunctionFullTests now also runs "bt" command before "py-bt-full",
similar to CFunctionTests which also runs "bt" command before
"py-bt". So test_gdb can skip the test if patterns like "?? ()" are
found in the gdb output.

(cherry picked from commit 1de9406)

Author: vstinner

Lib/test/test_gdb/test_cfunction_full.py

@@ -18,7 +18,7 @@ def check(self, func_name, cmd):
         gdb_output = self.get_stack_trace(
             cmd,
             breakpoint=func_name,
-            cmds_after_breakpoint=['py-bt-full'],
+            cmds_after_breakpoint=['bt', 'py-bt-full'],
             # bpo-45207: Ignore 'Function "meth_varargs" not
             # defined.' message in stderr.
             ignore_stderr=True,