Allow gap before first non-Lisp pseudovec member

Problem reported by Keith David Bershatsky in:
https://lists.gnu.org/r/emacs-devel/2019-04/msg00259.html
Solution suggested by Stefan Monnier in:
https://lists.gnu.org/r/emacs-devel/2019-04/msg00282.html
* src/buffer.h (BUFFER_LISP_SIZE): Simplify by using PSEUDOVECSIZE.
(BUFFER_REST_SIZE): Simplify by using VECSIZE and BUFFER_LISP_SIZE.
* src/lisp.h (PSEUDOVECSIZE): Base it on the last Lisp field,
not the first non-Lisp field.  All callers changed.  Callers
without Lisp fields changed to use ALLOCATE_PLAIN_PSEUDOVECTOR.
(ALLOCATE_PLAIN_PSEUDOVECTOR): New macro.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/thread.h b/src/thread.h
index 50f8f5cbe0a..0514669a87d 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -61,8 +61,8 @@ struct thread_state
   /* If we are waiting for some event, this holds the object we are
      waiting on.  */
   Lisp_Object event_object;
+  /* event_object must be the last Lisp field.  */
 
-  /* m_stack_bottom must be the first non-Lisp field.  */
   /* An address near the bottom of the stack.
      Tells GC how to save a copy of the stack.  */
   char const *m_stack_bottom;