Ensure that the gdb hooks can be installed when

srcdir != builddir.

Without this patch it is no longer possible to
build python when you don't run configure from
the root of the source tree.

Makefile.pre.in

@@ -442,7 +442,7 @@ libpython$(VERSION).sl: $(LIBRARY_OBJS)
 # to the stripped DWARF data for the shared library.
 gdbhooks: $(BUILDPYTHON)-gdb.py
 
-SRC_GDB_HOOKS=Tools/gdb/libpython.py
+SRC_GDB_HOOKS=$(srcdir)/Tools/gdb/libpython.py
 $(BUILDPYTHON)-gdb.py: $(SRC_GDB_HOOKS)
 	$(INSTALL_DATA) $(SRC_GDB_HOOKS) $(BUILDPYTHON)-gdb.py