cov: add some explicit includes that where missing

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

src/x86/intel_minnow_max.c

@@ -25,6 +25,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/utsname.h>
+#include <ctype.h>
 
 #include "common.h"
 #include "x86/intel_minnow_max.h"

src/x86/x86.c

@@ -23,6 +23,7 @@
  */
 
 #include <stdlib.h>
+#include <string.h>
 
 #include "mraa_internal.h"
 #include "x86/intel_galileo_rev_d.h"