[lldb] add --platform-available-ports option to the dotest.py (#112555)
This patch adds --platform-available-ports option to the dotest.py
script to avoid hardcoded gdb ports in lldb testsuite.
Currently, this option could be helpful in GdbRemoteTestCases (e.g.
TestLldbGdbServer, TestNonStop, TestGdbRemoteThreadsInStopReply,
TestGdbRemotePlatformFile, TestGdbRemote_vCont)