OpenBSD will kill any process that has %rsp outside of a MAP_STACK at syscall
or page fault. Upstream Wine doesn't mark its stacks.

Index: dlls/ntdll/unix/process.c
--- dlls/ntdll/unix/process.c.orig
+++ dlls/ntdll/unix/process.c
@@ -1816,6 +1816,9 @@ NTSTATUS WINAPI NtSetInformationProcess( HANDLE handle
                                        MEM_RESERVE, PAGE_READWRITE );
         if (!ret)
         {
+#ifdef __OpenBSD__
+            virtual_set_stack_mapping( addr, reserve );
+#endif
 #ifdef VALGRIND_STACK_REGISTER
             VALGRIND_STACK_REGISTER( addr, (char *)addr + reserve );
 #endif
