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

lldb/source/Core/ModuleList.cpp

@@ -26,6 +26,8 @@
 #include "lldb/Symbol/SymbolFile.h"
 #include "lldb/Symbol/VariableList.h"
 
+#include "llvm/Support/Threading.h"
+
 using namespace lldb;
 using namespace lldb_private;
 
@@ -644,8 +646,8 @@ size_t ModuleList::GetIndexForModule(const Module *module) const {
 
 static ModuleList &GetSharedModuleList() {
   static ModuleList *g_shared_module_list = nullptr;
-  static std::once_flag g_once_flag;
-  std::call_once(g_once_flag, []() {
+  static llvm::once_flag g_once_flag;
+  llvm::call_once(g_once_flag, []() {
     // NOTE: Intentionally leak the module list so a program doesn't have to
     // cleanup all modules and object files as it exits. This just wastes time
     // doing a bunch of cleanup that isn't required.