[clang][SPARC] Treat empty structs as if it's a one-bit type in the CC (#90338)

Make sure that empty structs are treated as if it has a size of one bit
in function parameters and return types so that it occupies a full
argument and/or return register slot.

This fixes crashes and miscompilations when passing and/or returning
empty structs.

Reviewed by: @s-barannikov