get_executable_path slight change to make it work under OpenBSD

(cherry picked from commit df87ad14d0be851ecdc02e592c3593b696762d26)

drivers/unix/os_unix.cpp

@@ -49,7 +49,7 @@
 #include <mach-o/dyld.h>
 #endif
 
-#ifdef __FreeBSD__
+#if defined(__FreeBSD__) || defined(__OpenBSD__)
 #include <sys/param.h>
 #endif
 #include "globals.h"
@@ -499,7 +499,7 @@ String OS_Unix::get_executable_path() const {
 		return OS::get_executable_path();
 	}
 	return b;
-#elif defined(__FreeBSD__)
+#elif defined(__FreeBSD__) || defined(__OpenBSD__)
 	char resolved_path[MAXPATHLEN];
 
 	realpath(OS::get_executable_path().utf8().get_data(), resolved_path);