otherwise makedev() function isnt found

Index: render/vulkan/vulkan.c
--- render/vulkan/vulkan.c.orig
+++ render/vulkan/vulkan.c
@@ -1,4 +1,4 @@
-#if defined(__FreeBSD__)
+#if defined(__FreeBSD__) || defined(__OpenBSD__)
 #undef _POSIX_C_SOURCE
 #endif
 #include <assert.h>
