Fix warnings reported by -Wpedantic

Previously CI hasn't been running with -Wpedantic (using autoconf), so
these haven't been reported previously.

- replace BUILD_ASSERT with static_assert()
- don't use %m GNU extension for printf
- don't use arithmetic on void*
- remove unused variables

Change-Id: I97d1acc908f06773b8b1ee95bfee80760fdc7a63
Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
diff --git a/utils/mctp-capture.h b/utils/mctp-capture.h
index e432df9..261caba 100644
--- a/utils/mctp-capture.h
+++ b/utils/mctp-capture.h
@@ -3,7 +3,9 @@
 #ifndef _UTILS_MCTP_CAPTURE_H
 #define _UTILS_MCTP_CAPTURE_H
 
+#ifdef HAVE_CONFIG_H
 #include "config.h"
+#endif
 
 #include "compiler.h"
 #include "libmctp.h"