[compiler-rt] [ASan][Windows] Fix false positive for zero sized rtl allocations (PR #181015)

[David Justo via llvm-commits]

================
@@ -40,8 +40,8 @@ int main() {
   if (!ptr2)
     return 1;
   size_t heapsize = HeapSize(GetProcessHeap(), 0, ptr2);
-  if (heapsize != 1) { // will be 0 without ASAN turned on
-    std::cerr << "HeapAlloc size failure! " << heapsize << " != 1\n";
+  if (heapsize != 0) {
+    std::cerr << "HeapAlloc size failure! " << heapsize << " != 0\n";
----------------
davidmrdavid wrote:

nit - in the preceding comment (lines ~22->~33), there's a bunch of preamble about how we now change zero-sized allocations to 1.

As a result, this changed check can appear surprising if we don't leave a comment saying that `HeapSize` will retrieve that user-provided size, not the internal 1-sized allocation.

So I recommend we add a comment :-) 

```suggestion
  // `HeapSize` will retrieve the user-defined size, not the _actual_ ASan-allocated size of '1'
  if (heapsize != 0) {
    std::cerr << "HeapAlloc size failure! " << heapsize << " != 0\n";
```

https://github.com/llvm/llvm-project/pull/181015