libgloss fix for bfin port

libgloss fix for bfin port

gcc-14 will complain loudly both for calling a function without an in-scope
prototype or when the in scope prototype differs from the known signature.

"main" happens to be one of the functions the compiler knows about.  So not
only do we need to prototype it, we need to make sure the prototype matches
what GCC thinks it should be.

This fixes the bfin libgloss port to do the right thing for bfin-elf.