fix target lib rebuilding

[Ian Lance Taylor]

Daniel Jacobowitz <drow@false.org> writes:

> Aha!  Thanks for clearing that up, Alexandre.  I still don't see how it
> happens (courtesy of .NOEXPORT), but I'll take your word for it.

By the way, you keep mentioning .NOEXPORT.  Although you still see
that in Makefiles quite a bit, it no longer has any effect on GNU
make.  GNU make no longer exports variables by default.  You can use
the special target .EXPORT_ALL_VARIABLES to get the old behaviour.

Ian