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, 2 insertions, 1 deletions

diff --git a/src/process.c b/src/process.c
index 802ac026249..6770a5ed884 100644
--- a/src/process.c
+++ b/src/process.c
@@ -858,7 +858,8 @@ allocate_pty (char pty_name[PTY_NAME_SIZE])
 static struct Lisp_Process *
 allocate_process (void)
 {
-  return ALLOCATE_ZEROED_PSEUDOVECTOR (struct Lisp_Process, pid, PVEC_PROCESS);
+  return ALLOCATE_ZEROED_PSEUDOVECTOR (struct Lisp_Process, thread,
+                                       PVEC_PROCESS);
 }
 
 static Lisp_Object