Our autoconf function "MYSQL_STACK_DIRECTION" will not work

correctly if the compiler optimizes too clever.

This has happaned on HP-UX 11.23 (IA64) at optimization
level "+O2", causing bug#42213:
   Check for "stack overrun" doesn't work, server crashes

Fix it by adding a pragma that prevents this optimization.
As a result, it should be safe to use "+O2" on this platform
(unless there is some other, optimizer-related, bug which
is just currently masked because we use resudec optimization).

config/ac-macros/misc.m4

@@ -583,6 +583,10 @@ fi
 AC_DEFUN([MYSQL_STACK_DIRECTION],
  [AC_CACHE_CHECK(stack direction for C alloca, ac_cv_c_stack_direction,
  [AC_TRY_RUN([#include <stdlib.h>
+ /* Prevent compiler optimization by HP's compiler, see bug#42213 */
+#if defined(__HP_cc) || defined (__HP_aCC) || defined (__hpux)
+#pragma noinline
+#endif
  int find_stack_direction ()
  {
    static char *addr = 0;