utils: Steal `steal` from libei

Add excerpt of `util-mem.h` from libei defining the macro `steal`, in
order to improve memory management and the code semantics.

See: 38132d6fc5/src/util-mem.h (L92)

src/util-mem.h

@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2020 Red Hat, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#pragma once
+
+#include "config.h"
+#include <stdlib.h>
+
+static inline void*
+_steal(void *ptr) {
+    void **original = (void**)ptr;
+    void *swapped = *original;
+    *original = NULL;
+    return swapped;
+}
+
+/**
+ * Resets the pointer content and resets the data to NULL.
+ */
+#ifdef _WIN32
+#define steal(ptr_) \
+    _steal(ptr_)
+#else
+#define steal(ptr_) \
+    (__typeof__(*ptr_))_steal(ptr_)
+#endif