LibSystem: Add pledge() and unveil() wrappers that return ErrorOr<void>

These will be more ergonomic to use together with TRY(). :^)

Userland/Libraries/LibSystem/Wrappers.cpp

@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibSystem/Wrappers.h>
+#include <LibSystem/syscall.h>
+
+namespace System {
+
+ErrorOr<void> pledge(StringView promises, StringView execpromises)
+{
+    Syscall::SC_pledge_params params {
+        { promises.characters_without_null_termination(), promises.length() },
+        { execpromises.characters_without_null_termination(), execpromises.length() },
+    };
+    int rc = syscall(SC_pledge, &params);
+    if (rc < 0)
+        return Error::from_errno(-rc);
+    return {};
+}
+
+ErrorOr<void> unveil(StringView path, StringView permissions)
+{
+    Syscall::SC_unveil_params params {
+        { path.characters_without_null_termination(), path.length() },
+        { permissions.characters_without_null_termination(), permissions.length() },
+    };
+    int rc = syscall(SC_unveil, &params);
+    if (rc < 0)
+        return Error::from_errno(-rc);
+    return {};
+}
+
+}