Issue 8287: try to fix the gdb-python install errors on Solaris

and FreeBSD.  Patch by Dave Malcolm.

Makefile.pre.in

@@ -442,8 +442,9 @@ libpython$(VERSION).sl: $(LIBRARY_OBJS)
 # to the stripped DWARF data for the shared library.
 gdbhooks: $(BUILDPYTHON)-gdb.py
 
-$(BUILDPYTHON)-gdb.py: Tools/gdb/libpython.py
-	$(INSTALL_DATA) $< $(BUILDPYTHON)-gdb.py
+SRC_GDB_HOOKS=Tools/gdb/libpython.py
+$(BUILDPYTHON)-gdb.py: $(SRC_GDB_HOOKS)
+	$(INSTALL_DATA) $(SRC_GDB_HOOKS) $(BUILDPYTHON)-gdb.py
 
 # This rule is here for OPENSTEP/Rhapsody/MacOSX. It builds a temporary
 # minimal framework (not including the Lib directory and such) in the current