Fix lifetime error in previous patch

Fix lifetime error in previous patch

Problem reported by Pip Cet in:
https://lists.gnu.org/r/emacs-devel/2019-07/msg00520.html
* src/alloc.c (inhibit_garbage_collection): Use new function.
(allow_garbage_collection): Accept intmax_t, not pointer.
* src/eval.c (default_toplevel_binding, do_one_unbind)
(backtrace_eval_unrewind, Fbacktrace__locals, mark_specpdl):
Support SPECPDL_UNWIND_INTMAX.
(record_unwind_protect_excursion): New function.
* src/lisp.h (enum specbind_tag): New constant SPECPDL_UNWIND_INTMAX.
(union specbinding): New member unwind_intmax.