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-internal.h

@@ -772,6 +772,30 @@ private:
   PyThreadState *m_save;
 };
 
+/* 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;
+};
+
 /* Use this after a TRY_EXCEPT to throw the appropriate Python
    exception.  */
 #define GDB_PY_HANDLE_EXCEPTION(Exception)	\