Fix secp256k1 build when only docker is available

Author: NyanCatTW1

coinlib/bin/docker_util.dart

@@ -25,7 +25,7 @@ Future<bool> dockerRun(
   // Build
   print("Building $tag");
   var exitCode = await execWithStdio(
-    dockerCmd, ["build", "-f", "-", "-t", tag],
+    dockerCmd, ["build", "-t", tag, "-"],
     stdin: dockerScript,
   );
 

coinlib/bin/util.dart

@@ -29,7 +29,11 @@ Future<int> execWithStdio(
     await process.stdin.close();
   }
 
-  await process.stdout.transform(utf8.decoder).forEach(stdout.write);
+  // Pipe stdout to terminal and discard stderr
+  await Future.wait([
+    process.stdout.transform(utf8.decoder).forEach(stdout.write),
+    process.stderr.drain<String?>(),
+  ]);
 
   return await process.exitCode;
 }