lib: Include compiler.h as early as is possible in the build

The compiler.h header provides us with some useful macro's
that we are using in the system.  We do not know exactly
where the CPP_NOTICE and CPP_WARN macros are used but
they can move around.  Place this header early in the
build then.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>

Author: donaldsharp

lib/zebra.h

@@ -379,6 +379,12 @@ struct in_pktinfo {
  */
 #define ZEBRA_HEADER_MARKER              254
 
+/*
+ * The compiler.h header is used for anyone using the CPP_NOTICE
+ * since this is universally needed, let's add it to zebra.h
+ */
+#include "compiler.h"
+
 /* Zebra route's types are defined in route_types.h */
 #include "route_types.h"