Prevent TestqOffsets.py picking up host binaries

Due to a fallback in GDBRemoteCommunicationClient.cpp, on Linux we
will assume a PID of 1 if the remote does not respond in some
way that tells us the real PID.

So if PID 1 happened to be a process that the current user could
read, we would try to debug that instead. On my current machine,
PID 1 was sshd run by root so we would ignore it. If I changed
the fallback to some process ID run by my user, the test would fail.

To prevent this, return something to LLDB that tells it there is
no remote PID, preventing the host lookup.

Fixes #155895

Author: DavidSpickett

lldb/test/API/functionalities/gdb_remote_client/TestqOffsets.py

@@ -10,6 +10,11 @@ class Responder(MockGDBServerResponder):
         def qOffsets(self):
             return "Text=470000;Data=470000"
 
+        def qfThreadInfo(self):
+            # Prevent LLDB defaulting to PID of 1 and looking up some other
+            # process when on an AArch64 host.
+            return "m-1"
+
     def test(self):
         self.server.responder = TestqOffsets.Responder()
         target = self.createTarget("qOffsets.yaml")