LRN: Add '-Wl,' prefix to -no-undefined

LRN: Add '-Wl,' prefix to -no-undefined

-no-undefined is not a valid compiler option as of GCC 4.6.x
(it IS valid linker option).
Note that this REQUIRES an extra -no-undefined to be passed to
libtool (this is done by GN_LIB_LDLFAGS and GN_PLUGIN_LDFLAGS),
because libtool does not understand -Wl,-no-undefined.