don't bother emitting a zero byte memset at all. We used to get them

in cases like this:

typedef struct {
  short instance;
  char name[0];
} ATTR_LIST_ENTRY2;

void test() {
  ATTR_LIST_ENTRY2 X = (ATTR_LIST_ENTRY2) { .instance = 7, };
}  

While it is safe to emit them, it is pretty silly.

llvm-svn: 69687