fixed OpenBSD support (#921)

Index: src/raw_logging.cc
--- src/raw_logging.cc.orig
+++ src/raw_logging.cc
@@ -59,7 +59,8 @@
 # include <unistd.h>
 #endif
 
-#if (defined(HAVE_SYSCALL_H) || defined(HAVE_SYS_SYSCALL_H)) && (!(defined(GLOG_OS_MACOSX)))
+#if (defined(HAVE_SYSCALL_H) || defined(HAVE_SYS_SYSCALL_H)) && \
+    (!(defined(GLOG_OS_MACOSX)) && !(defined(GLOG_OS_OPENBSD)))
 # define safe_write(fd, s, len)  syscall(SYS_write, fd, s, len)
 #else
   // Not so safe, but what can you do?