build: split buildflags package

Planned to be imported by nerdctl in future.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

util/buildflags/entitlements.go

@@ -0,0 +1,21 @@
+package buildflags
+
+import (
+	"github.com/moby/buildkit/util/entitlements"
+	"github.com/pkg/errors"
+)
+
+func ParseEntitlements(in []string) ([]entitlements.Entitlement, error) {
+	out := make([]entitlements.Entitlement, 0, len(in))
+	for _, v := range in {
+		switch v {
+		case "security.insecure":
+			out = append(out, entitlements.EntitlementSecurityInsecure)
+		case "network.host":
+			out = append(out, entitlements.EntitlementNetworkHost)
+		default:
+			return nil, errors.Errorf("invalid entitlement: %v", v)
+		}
+	}
+	return out, nil
+}