[X86_64] fix empty structure vaarg in c++ (#77907)

SizeInBytes of empty structure is 0 in C, while 1 in C++. And empty
structure argument of the function is ignored in X86_64 backend.As a
result, the value of variable arguments in C++ is incorrect. fix #77036

Co-authored-by: Longsheng Mou <moulongsheng@huawei.com>