common,w32: Implement globing of command line args.

* common/w32-misc.c [W32]: Include windows.h
(struct add_arg_s): New.
(add_arg): New.
(glob_arg): New.
(parse_cmdstring): Add arg argvflags and set it.
(w32_parse_commandline): Add arg r_itemsalloced.  Add globing.

* common/init.c (prepare_w32_commandline): Mark glob created items as
leaked.

* common/t-w32-cmdline.c : Include windows.h
(test_all): Add simple glob test for Unix.
(main): Add manual test mode for Windows.

* common/xasprintf.c (xtryreallocarray): New.
--

GnuPG-bug-id: 4398
Backported-from-master: 089c943967)

common/xasprintf.c

@@ -1,5 +1,6 @@
 /* xasprintf.c
  *	Copyright (C) 2003, 2005 Free Software Foundation, Inc.
+ *      Copyright (C) 2020 g10 Code GmbH
  *
  * This file is part of GnuPG.
  *
@@ -68,3 +69,55 @@ xtryasprintf (const char *fmt, ...)
     return NULL;
   return buf;
 }
+
+
+/* This is safe version of realloc useful for reallocing a calloced
+ * array.  There are two ways to call it:  The first example
+ * reallocates the array A to N elements each of SIZE but does not
+ * clear the newly allocated elements:
+ *
+ *  p = xtryreallocarray (a, n, n, nsize);
+ *
+ * Note that when NOLD is larger than N no cleaning is needed anyway.
+ * The second example reallocates an array of size NOLD to N elements
+ * each of SIZE but clear the newly allocated elements:
+ *
+ *  p = xtryreallocarray (a, nold, n, nsize);
+ *
+ * Note that xtryreallocarray (NULL, 0, n, nsize) is equivalent to
+ * xtrycalloc (n, nsize).
+ *
+ * The same function under the name gpgrt_reallocarray exists in
+ * libgpg-error but only since version 1.38 and thus we use a copy
+ * here.
+ */
+void *
+xtryreallocarray (void *a, size_t oldnmemb, size_t nmemb, size_t size)
+{
+  size_t oldbytes, bytes;
+  char *p;
+
+  bytes = nmemb * size; /* size_t is unsigned so the behavior on overflow
+                         * is defined. */
+  if (size && bytes / size != nmemb)
+    {
+      gpg_err_set_errno (ENOMEM);
+      return NULL;
+    }
+
+  p = xtryrealloc (a, bytes);
+  if (p && oldnmemb < nmemb)
+    {
+      /* OLDNMEMBS is lower than NMEMB thus the user asked for a
+         calloc.  Clear all newly allocated members.  */
+      oldbytes = oldnmemb * size;
+      if (size && oldbytes / size != oldnmemb)
+        {
+          xfree (p);
+          gpg_err_set_errno (ENOMEM);
+          return NULL;
+        }
+      memset (p + oldbytes, 0, bytes - oldbytes);
+    }
+  return p;
+}