The last two tests in the NotPresent test check for fixes that went into 5.3. Testing these against earlier runtimes will fail. Add availability checks so we only test when the fix is present.
While we're here, switch the symbolic references test to use indirect references. Direct references are very likely to pass the test even without the fix, as the reference is likely to point to readable memory. Indirect references make this much more likely to crash by then reading and dereferencing a pointer from the memory the relative pointer points to.
rdar://159034772
e1fff8127e