(LIBOBJS): Put @LIBOBJS@ into the make variable

LIBOBJS.
(CLEANFILES): Delete libnettle.so.
(clean-local): Delete the .lib linkfarm.
($(SHLIBFORLINK)): When building libnettle.so, create a link from
.lib/$SHLIBSONAME. Needed at runtime, for the testsuite.

Rev: src/nettle/Makefile.am:1.50