Fix interoperability test compilation on FreeBSD

Summary:
While building the 8.0 releases on FreeBSD, I encountered the following
error in the regression tests, where ompt/misc/interoperability.cpp
failed to compile, with:

```
projects/openmp/runtime/test/ompt/misc/interoperability.cpp:7:10: fatal error: 'alloca.h' file not found
#include <alloca.h>
         ^~~~~~~~~~
```

Like on NetBSD, alloca(3) is defined in <stdlib.h> instead.

Reviewers: emaste, jlpeyton, krytarowski, mgorny, protze.joachim

Reviewed By: jlpeyton

Subscribers: jdoerfert, openmp-commits

Tags: #openmp

Differential Revision: https://reviews.llvm.org/D59736

git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@356936 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/runtime/test/ompt/misc/interoperability.cpp b/runtime/test/ompt/misc/interoperability.cpp
index b07814e..927669e 100644
--- a/runtime/test/ompt/misc/interoperability.cpp
+++ b/runtime/test/ompt/misc/interoperability.cpp
@@ -3,7 +3,7 @@
 
 #include <iostream>
 #include <thread>
-#if !defined(__NetBSD__)
+#if !defined(__FreeBSD__) && !defined(__NetBSD__)
 #include <alloca.h>
 #else
 #include <cstdlib>