$OpenBSD$

Do this the non-np way (correct?).

Index: src/eval.cc
--- src/eval.cc.orig
+++ src/eval.cc
@@ -167,9 +167,8 @@ Evaluator::Evaluator()
   stack_addr_ = (char*)pthread_get_stackaddr_np(pthread_self()) - stack_size_;
 #else
   pthread_attr_t attr;
-  CHECK(pthread_getattr_np(pthread_self(), &attr) == 0);
-  CHECK(pthread_attr_getstack(&attr, &stack_addr_, &stack_size_) == 0);
-  CHECK(pthread_attr_destroy(&attr) == 0);
+  CHECK(pthread_attr_getstacksize(&attr, &stack_size_) == 0);
+  CHECK(pthread_attr_getstackaddr(&attr, &stack_addr_) == 0);
 #endif
 
   lowest_stack_ = (char*)stack_addr_ + stack_size_;
