[Support] Fix memory leak induced by sys::RemoveFileOnSignal (llvm#159984)

Before this PR, `FilesToRemove` was constructed but never deleted.

Author: aganea

llvm/lib/Support/Windows/Signals.inc

@@ -421,8 +421,13 @@ bool sys::RemoveFileOnSignal(StringRef Filename, std::string *ErrMsg) {
     return true;
   }
 
-  if (FilesToRemove == NULL)
+  if (FilesToRemove == NULL) {
     FilesToRemove = new std::vector<std::string>;
+    std::atexit([]() {
+      delete FilesToRemove;
+      FilesToRemove = NULL;
+    });
+  }
 
   FilesToRemove->push_back(std::string(Filename));