libc-hooks: Provide the 'open()' syscall

Some parts of Newlib, notably the locale handling stuff, will try to
call open(), and if it's not provided, any application that for some
reason is bringing in that code will fail to link.
Having a non-working implementation keeps that code working.

Change-Id: I28345dabb93431d6b80c839b23a46b7f99dc8734
Signed-off-by: Iván Briano <ivan.briano@intel.com>

lib/libc/newlib/libc-hooks.c

@@ -127,6 +127,11 @@ void _exit(int status)
 	}
 }
 
+int open(const char *name, int mode)
+{
+	return -1;
+}
+
 int close(int file)
 {
 	return -1;