lim_data too narrow

[James Van Artsdalen <james@jrv.org>]

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In GNU Emacs 21.3 (amd64--freebsd)

lim_data is too narrow to hold the size of the process data segment.
On my system (with 8 GB of RAM) the rlimit is by default (in KB):

$ ulimit -d
8388608

lim_data needs to be at least as wide as the rlimit .rlim_cur field or
truncation occurs.

I'm not sure what the right cross-platform portable way to detect this
situation is.  The patch below is an example.

Note that this change is not sufficient to build emacs for amd64.

*** mem-limits.h.~1~    Wed Mar  8 12:49:46 2000
--- mem-limits.h        Wed Dec 17 03:15:24 2003
***************
*** 98,104 ****
  static POINTER data_space_start;
  
  /* Number of bytes of writable memory we can expect to be able to get */
! static unsigned long lim_data;
  
  #ifdef NO_LIM_DATA
  static void
--- 98,104 ----
  static POINTER data_space_start;
  
  /* Number of bytes of writable memory we can expect to be able to get */
! static rlim_t lim_data;
  
  #ifdef NO_LIM_DATA
  static void