Import egg-secure-memory allocator from gcr

We can re-use the code inside gcr, as we know that it's working, tested,
and license compatible.

gtk/gtksecurememoryprivate.h

@@ -0,0 +1,95 @@
+/* gtksecurememoryprivate.h - Allocator for non-pageable memory
+
+   Copyright 2007  Stefan Walter
+   Copyright 2020  GNOME Foundation
+
+   SPDX-License-Identifier: LGPL-2.0-or-later
+
+   The Gnome Keyring Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Library General Public License as
+   published by the Free Software Foundation; either version 2 of the
+   License, or (at your option) any later version.
+
+   The Gnome Keyring Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Library General Public
+   License along with the Gnome Library; see the file COPYING.LIB.  If not,
+   see <http://www.gnu.org/licenses/>.
+
+   Author: Stef Walter <stef@memberwebs.com>
+*/
+
+#pragma once
+
+#include <stdlib.h>
+
+/*
+ * Main functionality
+ *
+ * Allocations return NULL on failure.
+ */
+
+#define GTK_SECURE_USE_FALLBACK     0x0001
+
+void *          gtk_secure_alloc_full   (const char *tag,
+                                         size_t length,
+                                         int options);
+
+void *          gtk_secure_realloc_full (const char *tag,
+                                         void *p,
+                                         size_t length,
+                                         int options);
+
+void            gtk_secure_free         (void *p);
+
+void            gtk_secure_free_full    (void *p,
+                                         int fallback);
+
+void            gtk_secure_clear        (void *p,
+                                         size_t length);
+
+int             gtk_secure_check        (const void *p);
+
+void            gtk_secure_validate     (void);
+
+char *          gtk_secure_strdup_full  (const char *tag,
+                                         const char *str,
+                                         int options);
+
+char *          gtk_secure_strndup_full (const char *tag,
+                                         const char *str,
+                                         size_t length,
+                                         int options);
+
+void            gtk_secure_strclear     (char *str);
+
+void            gtk_secure_strfree      (char *str);
+
+/* Simple wrappers */
+
+static inline void *gtk_secure_alloc (size_t length) {
+  return gtk_secure_alloc_full ("gtk", length, GTK_SECURE_USE_FALLBACK);
+}
+
+static inline void *gtk_secure_realloc (void *p, size_t length) {
+  return gtk_secure_realloc_full ("gtk", p, length, GTK_SECURE_USE_FALLBACK);
+}
+
+static inline void *gtk_secure_strdup (const char *str) {
+  return gtk_secure_strdup_full ("gtk", str, GTK_SECURE_USE_FALLBACK);
+}
+
+static inline void *gtk_secure_strndup (const char *str, size_t length) {
+  return gtk_secure_strndup_full ("gtk", str, length, GTK_SECURE_USE_FALLBACK);
+}
+
+typedef struct {
+  const char *tag;
+  size_t request_length;
+  size_t block_length;
+} gtk_secure_rec;
+
+gtk_secure_rec *   gtk_secure_records    (unsigned int *count);

gtk/meson.build

@@ -134,6 +134,7 @@ gtk_private_sources = files([
   'gtkscaler.c',
   'gtksearchengine.c',
   'gtksearchenginemodel.c',
+  'gtksecurememory.c',
   'gtksizerequestcache.c',
   'gtksortkeys.c',
   'gtkstyleanimation.c',