[lldb] Move ~Platform to source file

The called destructors of the members require the includes that are only
in the source file.

lldb/include/lldb/Target/Platform.h

@@ -75,7 +75,7 @@ public:
 
   /// The destructor is virtual since this class is designed to be inherited
   /// from by the plug-in instance.
-  ~Platform() override = default;
+  ~Platform() override;
 
   static void Initialize();
 

lldb/source/Target/Platform.cpp

@@ -395,6 +395,8 @@ Platform::Platform(bool is_host)
   LLDB_LOGF(log, "%p Platform::Platform()", static_cast<void *>(this));
 }
 
+Platform::~Platform() = default;
+
 void Platform::GetStatus(Stream &strm) {
   std::string s;
   strm.Printf("  Platform: %s\n", GetPluginName().GetCString());