Fix __builtin_assume_aligned incorrect type descriptor
example from @rsmith
struct A { int n; };
struct B { int n; };
struct C : A, B {};
void *f(C *c) {
// Incorrectly returns `c` rather than the address of the B base class.
return __builtin_assume_aligned((B*)c, 8);
}
Differential Revision: https://reviews.llvm.org/D133583
yronglin