building with mingw for windows

src/bignum.cpp

@@ -7,6 +7,7 @@
 
 #include "bignum.hpp"
 #include "buffer.hpp"
+#include "os.hpp"
 
 #include <assert.h>
 #include <math.h>
@@ -350,7 +351,7 @@ Buf *bignum_to_buf(BigNum *bn) {
         return buf_sprintf("%f", bn->data.x_float);
     } else {
         const char *neg = bn->is_negative ? "-" : "";
-        return buf_sprintf("%s%llu", neg, bn->data.x_uint);
+        return buf_sprintf("%s%" ZIG_PRI_llu "", neg, bn->data.x_uint);
     }
 }