Add blockheader_cgo file

Signed-off-by: Jakub Sztandera <kubuxu@protocol.ai>

chain/types/blockheader_cgo.go

@@ -0,0 +1,27 @@
+//+build cgo
+
+package types
+
+import (
+	"context"
+
+	"github.com/filecoin-project/go-address"
+	"go.opencensus.io/trace"
+	"golang.org/x/xerrors"
+)
+
+func (blk *BlockHeader) CheckBlockSignature(ctx context.Context, worker address.Address) error {
+	_, span := trace.StartSpan(ctx, "checkBlockSignature")
+	defer span.End()
+
+	if blk.BlockSig == nil {
+		return xerrors.New("block signature not present")
+	}
+
+	sigb, err := blk.SigningBytes()
+	if err != nil {
+		return xerrors.Errorf("failed to get block signing bytes: %w", err)
+	}
+
+	return blk.BlockSig.Verify(worker, sigb)
+}