[Plugin/Process] Use std::call_once() to initialize.

This replaces the home-grown initialization mechanism used before.

Differential Revision:  http://reviews.llvm.org/D8760	

llvm-svn: 233999
diff --git a/lldb/source/Plugins/Process/Linux/ProcessLinux.cpp b/lldb/source/Plugins/Process/Linux/ProcessLinux.cpp
index bc9e68a..7df3046 100644
--- a/lldb/source/Plugins/Process/Linux/ProcessLinux.cpp
+++ b/lldb/source/Plugins/Process/Linux/ProcessLinux.cpp
@@ -53,16 +53,14 @@
 void
 ProcessLinux::Initialize()
 {
-    static bool g_initialized = false;
+    static std::once_flag g_once_flag;
 
-    if (!g_initialized)
-    {
-        g_initialized = true;
+    std::call_once(g_once_flag, []() {
         PluginManager::RegisterPlugin(GetPluginNameStatic(),
                                       GetPluginDescriptionStatic(),
                                       CreateInstance);
         ProcessPOSIXLog::Initialize(GetPluginNameStatic());
-    }
+    });
 }
 
 //------------------------------------------------------------------------------