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/Host/linux/HostInfoLinux.cpp b/lldb/source/Host/linux/HostInfoLinux.cpp
index 2a01f06..1f39ca5 100644
--- a/lldb/source/Host/linux/HostInfoLinux.cpp
+++ b/lldb/source/Host/linux/HostInfoLinux.cpp
@@ -10,6 +10,8 @@
 #include "lldb/Host/linux/HostInfoLinux.h"
 #include "lldb/Core/Log.h"
 
+#include "llvm/Support/Threading.h"
+
 #include <limits.h>
 #include <stdio.h>
 #include <string.h>
@@ -44,8 +46,8 @@
 bool HostInfoLinux::GetOSVersion(uint32_t &major, uint32_t &minor,
                                  uint32_t &update) {
   static bool success = false;
-  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, []() {
 
     struct utsname un;
     if (uname(&un) == 0) {
@@ -100,8 +102,8 @@
 llvm::StringRef HostInfoLinux::GetDistributionId() {
   // Try to run 'lbs_release -i', and use that response
   // for the distribution id.
-  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, []() {
 
     Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_HOST));
     if (log)