Add include for strncasecmp

Index: pinentry/pinentry.c
--- pinentry/pinentry.c.orig
+++ pinentry/pinentry.c
@@ -19,6 +19,7 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <strings.h>
 #include <unistd.h>
 #include <assert.h>
 
