Remove dependency on glibc malloc internals.

Remove dependency on glibc malloc internals.

* alloc.c (XMALLOC_OVERRUN_CHECK_OVERHEAD, XMALLOC_OVERRUN_CHECK_SIZE):
Move back here from lisp.h, but with their new implementations.
(XMALLOC_BASE_ALIGNMENT, COMMON_MULTIPLE, XMALLOC_HEADER_ALIGNMENT)
(XMALLOC_OVERRUN_SIZE_SIZE): Move these new lisp.h macros here.
* charset.c (charset_table_init): New static var.
(syms_of_charset): Use it instead of xmalloc.  This removes a
dependency on glibc malloc internals.  See Eli Zaretskii's comment in
<http://lists.gnu.org/archive/html/emacs-devel/2011-09/msg00815.html>.
* lisp.h (XMALLOC_OVERRUN_CHECK_OVERHEAD, XMALLOC_OVERRUN_CHECK_SIZE):
Move back to alloc.c.
(XMALLOC_BASE_ALIGNMENT, COMMON_MULTIPLE, XMALLOC_HEADER_ALIGNMENT)
(XMALLOC_OVERRUN_SIZE_SIZE): Move to alloc.c.