[lldb][test] Implement getting thread ID on OpenBSD (llvm#71129)

Author: brad0

lldb/packages/Python/lldbsuite/test/make/thread.h

@@ -13,6 +13,8 @@ int pthread_threadid_np(pthread_t, __uint64_t *);
 #include <pthread_np.h>
 #elif defined(__NetBSD__)
 #include <lwp.h>
+#elif defined(__OpenBSD__)
+#include <unistd.h>
 #elif defined(_WIN32)
 #include <windows.h>
 #endif
@@ -29,6 +31,8 @@ inline uint64_t get_thread_id() {
 #elif defined(__NetBSD__)
   // Technically lwpid_t is 32-bit signed integer
   return static_cast<uint64_t>(_lwp_self());
+#elif defined(__OpenBSD__)
+  return static_cast<uint64_t>(getthrid());
 #elif defined(_WIN32)
   return static_cast<uint64_t>(::GetCurrentThreadId());
 #else