[lldb][test] Add extra logging for module cache test

And remove the workaround I was trying, as this logging may prove what
the actual issue is.

Which I think is that the thread plan map in Process is cleared before
the threads are destroyed. So Thread::ShouldStop could be getting
the current plan, then the plan map is cleared, then Thread::ShouldStop
is deciding based on that plan to pop a plan from the now empty stack.

lldb/test/API/python_api/global_module_cache/TestGlobalModuleCache.py

@@ -34,6 +34,10 @@ class GlobalModuleCacheTestCase(TestBase):
     # The rerun tests indicate rerunning on Windows doesn't really work, so
     # this one won't either.
     @skipIfWindows
+    # On Arm and AArch64 Linux, this test attempts to pop a thread plan when
+    # we only have the base plan remaining. Skip it until we can figure out
+    # the bug this is exposing.
+    @skipIf(oslist=["linux"], archs=["arm", "aarch64"])
     def test_OneTargetOneDebugger(self):
         self.do_test(True, True)
 
@@ -50,6 +54,11 @@ class GlobalModuleCacheTestCase(TestBase):
         self.do_test(True, False)
 
     def do_test(self, one_target, one_debugger):
+        # Here to debug flakiness on Arm, remove later!
+        log_cmd_result = lldb.SBCommandReturnObject()
+        interp = self.dbg.GetCommandInterpreter()
+        interp.HandleCommand("log enable lldb step", log_cmd_result)
+
         # Make sure that if we have one target, and we run, then
         # change the binary and rerun, the binary (and any .o files
         # if using dwarf in .o file debugging) get removed from the
@@ -100,13 +109,6 @@ class GlobalModuleCacheTestCase(TestBase):
                 self.old_debugger = self.dbg
                 self.dbg = new_debugger
                 def cleanupDebugger(self):
-                    # On Arm and AArch64 Linux, it is suspected that destroying
-                    # the debugger first causes lldb to try to pop from an empty
-                    # thread plan stack. Try to prove this by killing the process
-                    # first.
-                    for i in range(self.dbg.GetNumTargets()):
-                        self.dbg.GetTargetAtIndex(i).GetProcess().Kill()
-
                     lldb.SBDebugger.Destroy(self.dbg)
                     self.dbg = self.old_debugger
                     self.old_debugger = None