macro to add this library to, to prevent it from being
automatically linked to all binaries. This should fix the Win32
build of loaddrv.
* Makefile.am (avrdude_LDADD): add LIBUSB here.
git-svn-id: svn://svn.savannah.nongnu.org/avrdude/trunk@602 81a1dc3b-b13d-400b-aceb-764788c761c2