[X86_64] fix arg pass error in struct. (#86902)
```
typedef long long t67 __attribute__((aligned (4)));
struct s67 {
int a;
t67 b;
};
void f67(struct s67 x) {
}
```
When classify:
a: Lo = Integer, Hi = NoClass
b: Lo = Integer, Hi = NoClass
struct S: Lo = Integer, Hi = NoClass
```
define dso_local void @f67(i64 %x.coerce) {
```
In this case, only one i64 register is used when the structure parameter
is transferred, which is obviously incorrect.So we need to treat the
split case specially. fix
https://github.com/llvm/llvm-project/issues/85387.
