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/Core/Debugger.cpp b/lldb/source/Core/Debugger.cpp
index 420cb41..bbcbc8e 100644
--- a/lldb/source/Core/Debugger.cpp
+++ b/lldb/source/Core/Debugger.cpp
@@ -17,6 +17,7 @@
 // Other libraries and framework includes
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/DynamicLibrary.h"
+#include "llvm/Support/Threading.h"
 
 // Project includes
 #include "lldb/Core/FormatEntity.h"
@@ -762,7 +763,7 @@
   //     static void Debugger::Destroy(lldb::DebuggerSP &debugger_sp);
   //     static void Debugger::Terminate();
   //----------------------------------------------------------------------
-  std::call_once(m_clear_once, [this]() {
+  llvm::call_once(m_clear_once, [this]() {
     ClearIOHandlers();
     StopIOHandlerThread();
     StopEventHandlerThread();