wldbg: add WLDBG_UNUSED macro
wldbg: add WLDBG_UNUSED macro

this expands to __attribute__((unused)). This is useful in passes,
because not in all passes we use all arguments and the compiler
flood us with warnings - which are useful otherwise. So if we know
that we do not use particular parametr, we can mark it as WLDBG_UNUSED

mchalupa/wldbg,mchalupa/wldbg