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, 3 deletions

diff --git a/src/process.h b/src/process.h
index d66aa062a54..5e957c4298e 100644
--- a/src/process.h
+++ b/src/process.h
@@ -117,9 +117,7 @@ struct Lisp_Process
 
     /* The thread a process is linked to, or nil for any thread.  */
     Lisp_Object thread;
-
-    /* After this point, there are no Lisp_Objects any more.  */
-    /* alloc.c assumes that `pid' is the first such non-Lisp slot.  */
+    /* After this point, there are no Lisp_Objects.  */
 
     /* Process ID.  A positive value is a child process ID.
        Zero is for pseudo-processes such as network or serial connections,