[compiler-rt] Reland "[rtsan] Intercept aligned_alloc on all versions of OSX if available on the build machine" (PR #114153)

[Chris Apple via llvm-commits]

================
@@ -464,10 +464,13 @@ INTERCEPTOR(void *, valloc, SIZE_T size) {
 }
 
 #if SANITIZER_INTERCEPT_ALIGNED_ALLOC
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunguarded-availability-new"
----------------
cjappl wrote:

https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html

This documentation may be helpful.


My understanding below:

If code that is **built** on a build machine that is aware of `aligned_alloc`, and the binary has a function that calls it "unguarded":

```cpp
int main() 
{
    aligned_alloc(alignof(int), sizeof(int)); 
}

```

It will crash when it **runs** on systems that do not have this function defined (OSX < 10.15)

You can get around this by guarding it:
```
int main() 
{
    if (__builtin_available(macOS 10.15, *))
        aligned_alloc(alignof(int), sizeof(int)); 
    else 
       malloc(sizeof(int));
}
```

In this PR we add aligned_alloc as a weak import so it will link on our build machine, if the build machine is 10.15 or greater (aware of the symbol `__MAC_10_15`). This is necessary because the OS version we build for is min version 10.13.

We define the interceptor function, and turn of the unguarded warning, so if a client machine has `aligned_alloc` it will be intercepted.

If the client machine does not have `aligned_alloc` (<10.15), it will not have `aligned_alloc` (a little circular logic, for you), and we will never intercept anything, so us defining this interceptor will have no effect and cause no issue

https://github.com/llvm/llvm-project/pull/114153