Better heuristic for C stack overflow

Improve the heuristic for distinguishing stack overflows from
other SIGSEGV causes (Bug#21004).  Corinna Vinschen explained that
the getrlimit method wasn't portable to Cygwin; see:
https://www.cygwin.com/ml/cygwin/2015-07/msg00092.html
Corinna suggested pthread_getattr_np but this also has problems.
Instead, replace the low-level system stuff with a simple
heuristic based on known good stack addresses.
* src/eval.c, src/lisp.h (near_C_stack_top): New function.
* src/sysdep.c: Don't include <sys/resource.h>.
(stack_direction): Remove.  All uses removed.
(stack_overflow): New function.
(handle_sigsegv): Use it instead of incorrect getrlimit heuristic.
Make SEGV fatal in non-main threads.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/lisp.h b/src/lisp.h
index c3289c9d700..341603f311f 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4029,6 +4029,7 @@ extern _Noreturn void verror (const char *, va_list)
   ATTRIBUTE_FORMAT_PRINTF (1, 0);
 extern void un_autoload (Lisp_Object);
 extern Lisp_Object call_debugger (Lisp_Object arg);
+extern void *near_C_stack_top (void);
 extern void init_eval_once (void);
 extern Lisp_Object safe_call (ptrdiff_t, Lisp_Object, ...);
 extern Lisp_Object safe_call1 (Lisp_Object, Lisp_Object);