bpo-38965: Fix faulthandler._stack_overflow() on GCC 10 (GH-17467) (GH-28079)

Use the "volatile" keyword to prevent tail call optimization on any compiler, rather than relying on compiler specific pragma. (cherry picked from commit 8b78796) Co-authored-by: Victor Stinner <vstinner@python.org> (cherry picked from commit 5044c88) Co-authored-by: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com>

Author: miss-islington

Misc/NEWS.d/next/Tests/2019-12-04-17-08-55.bpo-38965.yqax3m.rst

@@ -0,0 +1,3 @@
+Fix test_faulthandler on GCC 10. Use the "volatile" keyword in
+``faulthandler._stack_overflow()`` to prevent tail call optimization on any
+compiler, rather than relying on compiler specific pragma.

Modules/faulthandler.c

@@ -1091,18 +1091,14 @@ faulthandler_fatal_error_py(PyObject *self, PyObject *args)
 #if defined(HAVE_SIGALTSTACK) && defined(HAVE_SIGACTION)
 #define FAULTHANDLER_STACK_OVERFLOW
 
-#ifdef __INTEL_COMPILER
- /* Issue #23654: Turn off ICC's tail call optimization for the
- * stack_overflow generator. ICC turns the recursive tail call into
- * a loop. */
-# pragma intel optimization_level 0
-#endif
-static
-uintptr_t
+static uintptr_t
 stack_overflow(uintptr_t min_sp, uintptr_t max_sp, size_t *depth)
 {
- /* allocate 4096 bytes on the stack at each call */
- unsigned char buffer[4096];
+ /* Allocate (at least) 4096 bytes on the stack at each call.
+
+ bpo-23654, bpo-38965: use volatile keyword to prevent tail call
+ optimization. */
+ volatile unsigned char buffer[4096];
  uintptr_t sp = (uintptr_t)&buffer;
  *depth += 1;
  if (sp < min_sp || max_sp < sp)