[X86_32][C++] fix 0 sized struct case in vaarg. (#86388)
struct SuperEmpty { struct{ int a[0];} b;};
Such 0 sized structs in c++ mode can not be ignored in i386 for that c++
fields are never empty.But when EmitVAArg, its size is 0, so that
va_list not increase.Maybe we can just Ignore this kind of arguments,
like X86_64 did. Fix #86385.
