[debugserver] Migrate RNBRemote away from PThreadMutex (NFC) (#137547)

The debugserver code predates modern C++, but with C++11 and later
there's no need to have something like PThreadMutex. This migrates
RNBRemote away from PThreadMutex in preparation for removing it.

Author: JDevlieghere

lldb/tools/debugserver/source/RNBRemote.cpp

@@ -820,7 +820,7 @@ rnb_err_t RNBRemote::GetPacketPayload(std::string &return_packet) {
   // (uint32_t)m_comm.Timer().ElapsedMicroSeconds(true), __FUNCTION__);
 
   {
-    PThreadMutex::Locker locker(m_mutex);
+    std::lock_guard<std::mutex> guard(m_mutex);
     if (m_rx_packets.empty()) {
       // Only reset the remote command available event if we have no more
       // packets
@@ -1052,7 +1052,7 @@ void RNBRemote::CommDataReceived(const std::string &new_data) {
   //  (uint32_t)m_comm.Timer().ElapsedMicroSeconds(true), __FUNCTION__);
 
   // Put the packet data into the buffer in a thread safe fashion
-  PThreadMutex::Locker locker(m_mutex);
+  std::lock_guard<std::mutex> guard(m_mutex);
 
   std::string data;
   // See if we have any left over data from a previous call to this

lldb/tools/debugserver/source/RNBRemote.h

@@ -14,7 +14,6 @@
 #define LLDB_TOOLS_DEBUGSERVER_SOURCE_RNBREMOTE_H
 
 #include "DNB.h"
-#include "PThreadMutex.h"
 #include "RNBContext.h"
 #include "RNBDefs.h"
 #include "RNBSocket.h"
@@ -25,7 +24,6 @@
 
 class RNBSocket;
 class RNBContext;
-class PThreadEvents;
 
 enum event_loop_mode { debug_nub, gdb_remote_protocol, done };
 
@@ -379,7 +377,7 @@ class RNBRemote {
   std::string m_arch;
   nub_thread_t m_continue_thread; // thread to continue; 0 for any, -1 for all
   nub_thread_t m_thread;          // thread for other ops; 0 for any, -1 for all
-  PThreadMutex m_mutex;           // Mutex that protects
+  std::mutex m_mutex;             // Mutex that protects
   DispatchQueueOffsets m_dispatch_queue_offsets;
   nub_addr_t m_dispatch_queue_offsets_addr;
   uint32_t m_qSymbol_index;