cmocka: Include strings.h for strcasecmp

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
diff --git a/src/cmocka.c b/src/cmocka.c
index e43a8b3..4a1a613 100644
--- a/src/cmocka.c
+++ b/src/cmocka.c
@@ -31,6 +31,10 @@
 #include <signal.h>
 #endif
 
+#ifdef HAVE_STRINGS_H
+#include <strings.h>
+#endif
+
 #include <stdint.h>
 #include <setjmp.h>
 #include <stdarg.h>