[Windows] Introduce a switch for the lldb-server mode on Windows

Summary:
This patch introduces a switch, based on the environment variable
`LLDB_USE_LLDB_SERVER`, to determine whether to use the `ProcessWindows` plugin
(the old way) or the `lldb-server` way for debugging on Windows.

Reviewers: labath, amccarth, asmith, stella.stamenova

Reviewed By: labath, amccarth

Subscribers: mstorsjo, abidh, JDevlieghere, lldb-commits, leonid.mashinskiy

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D68258

llvm-svn: 374325

Author: Aleksandr Urakov

lldb/source/Plugins/Process/Windows/Common/ProcessWindows.cpp

@@ -81,13 +81,24 @@ ProcessSP ProcessWindows::CreateInstance(lldb::TargetSP target_sp,
   return ProcessSP(new ProcessWindows(target_sp, listener_sp));
 }
 
-void ProcessWindows::Initialize() {
-  static llvm::once_flag g_once_flag;
+static bool ShouldUseLLDBServer() {
+  llvm::StringRef use_lldb_server = ::getenv("LLDB_USE_LLDB_SERVER");
+  return use_lldb_server.equals_lower("on") ||
+         use_lldb_server.equals_lower("yes") ||
+         use_lldb_server.equals_lower("1") ||
+         use_lldb_server.equals_lower("true");
+}
 
-  llvm::call_once(g_once_flag, []() {
-    PluginManager::RegisterPlugin(GetPluginNameStatic(),
-                                  GetPluginDescriptionStatic(), CreateInstance);
-  });
+void ProcessWindows::Initialize() {
+  if (!ShouldUseLLDBServer()) {
+    static llvm::once_flag g_once_flag;
+
+    llvm::call_once(g_once_flag, []() {
+      PluginManager::RegisterPlugin(GetPluginNameStatic(),
+                                    GetPluginDescriptionStatic(),
+                                    CreateInstance);
+    });
+  }
 }
 
 void ProcessWindows::Terminate() {}