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/MacOSX-Kernel/ProcessKDP.cpp b/lldb/source/Plugins/Process/MacOSX-Kernel/ProcessKDP.cpp
index a757bba..121418d 100644
--- a/lldb/source/Plugins/Process/MacOSX-Kernel/ProcessKDP.cpp
+++ b/lldb/source/Plugins/Process/MacOSX-Kernel/ProcessKDP.cpp
@@ -39,6 +39,8 @@
 #include "lldb/Target/Thread.h"
 #include "lldb/Utility/StringExtractor.h"
 
+#include "llvm/Support/Threading.h"
+
 #define USEC_PER_SEC 1000000
 
 // Project includes
@@ -718,9 +720,9 @@
 }
 
 void ProcessKDP::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);