gdb: move gdbpy_gil into python-internal.h

Move gdbpy_gil class into python-internal.h, the next
commit wants to make use of this class from a file other
than python.c.

Approved-By: Tom Tromey <tom@tromey.com>

gdb/python/python.c

@@ -264,30 +264,6 @@ gdbpy_enter::finalize ()
   python_gdbarch = current_inferior ()->arch ();
 }
 
-/* A helper class to save and restore the GIL, but without touching
-   the other globals that are handled by gdbpy_enter.  */
-
-class gdbpy_gil
-{
-public:
-
-  gdbpy_gil ()
-    : m_state (PyGILState_Ensure ())
-  {
-  }
-
-  ~gdbpy_gil ()
-  {
-    PyGILState_Release (m_state);
-  }
-
-  DISABLE_COPY_AND_ASSIGN (gdbpy_gil);
-
-private:
-
-  PyGILState_STATE m_state;
-};
-
 /* Set the quit flag.  */
 
 static void