[TySan] Type aliasing violations not detected on returned struct.

[BStott6]

Reproducer (C):

struct S {
    int a;
    float b;
};

struct S returns_s(void) {
    struct S x;
    x.a = 1;
    x.b = 1.0f;
    return x;
}

int main(void) {
    struct S x = returns_s();

    // This should produce an aliasing violation.
    float aliased = *((float *) &x.a);
}

When compiled with clang -fsanitize=type, the sanitizer does not catch the type aliasing violation reading x.a through a float pointer. If x has its members assigned in main, then the aliasing violation is correctly reported.