GHOST: Only spam about X11 errors when using --debug-ghost

This commit adds a new command line argument --debug-ghost and
makes it so X11 errors happening during context initialization
are only printed when this new flag is sued.

There is no need to flood users with errors when their GPU is
not supporting latest OpenGL version. Or, at a very minimum,
the error must be more meaning full.

Differential Revision: https://developer.blender.org/D6057

intern/ghost/intern/GHOST_System.cpp

@@ -46,7 +46,8 @@ GHOST_System::GHOST_System()
 #ifdef WITH_INPUT_NDOF
       m_ndofManager(0),
 #endif
-      m_tabletAPI(GHOST_kTabletAutomatic)
+      m_tabletAPI(GHOST_kTabletAutomatic),
+      m_is_debug_enabled(false)
 {
 }
 
@@ -388,3 +389,13 @@ void GHOST_System::useWindowFocus(const bool use_focus)
 {
   m_windowFocus = use_focus;
 }
+
+void GHOST_System::initDebug(bool is_debug_enabled)
+{
+  m_is_debug_enabled = is_debug_enabled;
+}
+
+bool GHOST_System::isDebugEnabled()
+{
+  return m_is_debug_enabled;
+}