[recipes] Fix the build on OpenBSD

[Matthias Clasen <matthiasc src gnome org>]

commit f255a2322c0d386e1695282a2df8a5019655bc4d
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Nov 4 13:53:02 2017 -0400

    Fix the build on OpenBSD
    
    O_PATH is Linux-only. Not sure the email portal has a chance
    of working without it, but we can at last make the build
    succeed.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=789812

 src/gr-mail.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/src/gr-mail.c b/src/gr-mail.c
index 1aa47f6..9fad60c 100644
--- a/src/gr-mail.c
+++ b/src/gr-mail.c
@@ -32,6 +32,10 @@
 #include "gr-mail.h"
 #include "gr-utils.h"
 
+#ifndef O_PATH
+#define O_PATH 0
+#endif
+
 typedef struct {
         GtkWindow *window;
         char *handle;