Switch std::call_once to llvm::call_once

Summary:
The std::call_once implementation in libstdc++ has problems on few systems: NetBSD, OpenBSD and Linux PPC. LLVM ships with a homegrown implementation llvm::call_once to help on these platforms.

This change is required in the NetBSD LLDB port. std::call_once with libstdc++ results with crashing the debugger.

Sponsored by <The NetBSD Foundation>

Reviewers: labath, joerg, emaste, mehdi_amini, clayborg

Reviewed By: labath, clayborg

Subscribers: #lldb

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D29288

llvm-svn: 294202
diff --git a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
index 6766da9..122cd9f 100644
--- a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
@@ -81,6 +81,7 @@
 
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/Threading.h"
 
 #define DEBUGSERVER_BASENAME "debugserver"
 using namespace lldb;
@@ -3434,9 +3435,9 @@
 }
 
 void ProcessGDBRemote::Initialize() {
-  static std::once_flag g_once_flag;
+  static llvm::once_flag g_once_flag;
 
-  std::call_once(g_once_flag, []() {
+  llvm::call_once(g_once_flag, []() {
     PluginManager::RegisterPlugin(GetPluginNameStatic(),
                                   GetPluginDescriptionStatic(), CreateInstance,
                                   DebuggerInitialize);