use freestanding headers

core/print.c

@@ -5,8 +5,8 @@
 #include <stdarg.h>
 #include <stddef.h>
 #include <stdint.h>
-#include <stdlib.h>
-#include <string.h>
+#include <zinnia/stdlib.h>
+#include <zinnia/string.h>
 
 typedef void (*log_fn_t)(void* ctx, const char* buf, size_t len);