Move gdb obstack code to gdbsupport

This moves the gdb-specific obstack code -- both extensions like
obconcat and obstack_strdup, and things like auto_obstack -- to
gdbsupport.

gdbsupport/gdb_obstack.h

@@ -0,0 +1,156 @@
+/* Obstack wrapper for GDB.
+
+   Copyright (C) 2002-2022 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#if !defined (GDB_OBSTACK_H)
+#define GDB_OBSTACK_H 1
+
+#include "obstack.h"
+
+/* Utility macros - wrap obstack alloc into something more robust.  */
+
+template <typename T>
+static inline T*
+obstack_zalloc (struct obstack *ob)
+{
+  static_assert (IsMallocable<T>::value, "Trying to use OBSTACK_ZALLOC with a \
+non-POD data type.  Use obstack_new instead.");
+  return ((T *) memset (obstack_alloc (ob, sizeof (T)), 0, sizeof (T)));
+}
+
+#define OBSTACK_ZALLOC(OBSTACK,TYPE) obstack_zalloc<TYPE> ((OBSTACK))
+
+template <typename T>
+static inline T *
+obstack_calloc (struct obstack *ob, size_t number)
+{
+  static_assert (IsMallocable<T>::value, "Trying to use OBSTACK_CALLOC with a \
+non-POD data type.  Use obstack_new instead.");
+  return ((T *) memset (obstack_alloc (ob, number * sizeof (T)), 0,
+			number * sizeof (T)));
+}
+
+#define OBSTACK_CALLOC(OBSTACK,NUMBER,TYPE) \
+  obstack_calloc<TYPE> ((OBSTACK), (NUMBER))
+
+/* Allocate an object on OB and call its constructor.  */
+
+template <typename T, typename... Args>
+static inline T*
+obstack_new (struct obstack *ob, Args&&... args)
+{
+  T* object = (T *) obstack_alloc (ob, sizeof (T));
+  object = new (object) T (std::forward<Args> (args)...);
+  return object;
+}
+
+/* Unless explicitly specified, GDB obstacks always use xmalloc() and
+   xfree().  */
+/* Note: ezannoni 2004-02-09: One could also specify the allocation
+   functions using a special init function for each obstack,
+   obstack_specify_allocation.  However we just use obstack_init and
+   let these defines here do the job.  While one could argue the
+   superiority of one approach over the other, we just chose one
+   throughout.  */
+
+#define obstack_chunk_alloc xmalloc
+#define obstack_chunk_free xfree
+
+#define obstack_grow_str(OBSTACK,STRING) \
+  obstack_grow (OBSTACK, STRING, strlen (STRING))
+#define obstack_grow_str0(OBSTACK,STRING) \
+  obstack_grow0 (OBSTACK, STRING, strlen (STRING))
+
+#define obstack_grow_wstr(OBSTACK, WSTRING) \
+  obstack_grow (OBSTACK, WSTRING, sizeof (gdb_wchar_t) * gdb_wcslen (WSTRING))
+
+/* Concatenate NULL terminated variable argument list of `const char
+   *' strings; return the new string.  Space is found in the OBSTACKP.
+   Argument list must be terminated by a sentinel expression `(char *)
+   NULL'.  */
+
+extern char *obconcat (struct obstack *obstackp, ...) ATTRIBUTE_SENTINEL;
+
+/* Duplicate STRING, returning an equivalent string that's allocated on the
+   obstack OBSTACKP.  */
+
+static inline char *
+obstack_strdup (struct obstack *obstackp, const char *string)
+{
+  return (char *) obstack_copy0 (obstackp, string, strlen (string));
+}
+
+/* Duplicate STRING, returning an equivalent string that's allocated on the
+   obstack OBSTACKP.  */
+
+static inline char *
+obstack_strdup (struct obstack *obstackp, const std::string &string)
+{
+  return (char *) obstack_copy0 (obstackp, string.c_str (),
+				 string.size ());
+}
+
+/* Duplicate the first N characters of STRING, returning a
+   \0-terminated string that's allocated on the obstack OBSTACKP.
+   Note that exactly N characters are copied, even if STRING is
+   shorter.  */
+
+static inline char *
+obstack_strndup (struct obstack *obstackp, const char *string, size_t n)
+{
+  return (char *) obstack_copy0 (obstackp, string, n);
+}
+
+/* An obstack that frees itself on scope exit.  */
+struct auto_obstack : obstack
+{
+  auto_obstack ()
+  { obstack_init (this); }
+
+  ~auto_obstack ()
+  { obstack_free (this, NULL); }
+
+  DISABLE_COPY_AND_ASSIGN (auto_obstack);
+
+  /* Free all memory in the obstack but leave it valid for further
+     allocation.  */
+  void clear ()
+  { obstack_free (this, obstack_base (this)); }
+};
+
+/* Objects are allocated on obstack instead of heap.  */
+
+struct allocate_on_obstack
+{
+  allocate_on_obstack () = default;
+
+  void* operator new (size_t size, struct obstack *obstack)
+  {
+    return obstack_alloc (obstack, size);
+  }
+
+  void* operator new[] (size_t size, struct obstack *obstack)
+  {
+    return obstack_alloc (obstack, size);
+  }
+
+  void operator delete (void *memory) {}
+  void operator delete[] (void *memory) {}
+};
+
+#endif