BFD: disable gcc6 warnings in helper macros

Change-Id: Ibec3f1a2619d593accd8c560fb29d39d5617e16a
Signed-off-by: Klement Sekera <ksekera@cisco.com>
diff --git a/src/vnet/bfd/bfd_cli.c b/src/vnet/bfd/bfd_cli.c
index 44e671c..b2cd8df 100644
--- a/src/vnet/bfd/bfd_cli.c
+++ b/src/vnet/bfd/bfd_cli.c
@@ -385,8 +385,19 @@
       have_##n = 1;                            \
     }
 
+#if __GNUC__ >= 6
+#define PRAGMA_STR1 \
+  _Pragma ("GCC diagnostic ignored \"-Wtautological-compare\"");
+#define PRAGMA_STR2 _Pragma ("GCC diagnostic pop");
+#else
+#define PRAGMA_STR1
+#define PRAGMA_STR2
+#endif
+
 #define CHECK_MANDATORY(t, n, s, r, ...)                                  \
+  PRAGMA_STR1                                                             \
   if (mandatory == r && !have_##n)                                        \
+    PRAGMA_STR2                                                           \
     {                                                                     \
       ret = clib_error_return (0, "Required parameter `%s' missing.", s); \
       goto out;                                                           \