This should allow to keep the libtool options all in one place and at
the same time define different options depending on the host.
Made sure that -no-undefined is set only on Win32. Although no side
effects on Linux and OSX have been observed so far, it's probably better
to play it safe; it does not seem to be needed/does not seem to matter on *nix,
only required for Win32.
jin-eld
ed1c130ebc