Implement process_madvise support.

Add opt.process_madvise_max_batch which determines if process_madvise is enabled
(non-zero) and the max # of regions in each batch.  Added another limiting
factor which is the space to reserve on stack, which results in the max batch of
128.

configure.ac

@@ -2544,6 +2544,17 @@ if test "x${je_cv_madvise}" = "xyes" ; then
   if test "x${je_cv_madv_collapse}" = "xyes" ; then
     AC_DEFINE([JEMALLOC_HAVE_MADVISE_COLLAPSE], [ ], [ ])
   fi
+
+  dnl Check for process_madvise
+  JE_COMPILABLE([process_madvise(2)], [
+#include <sys/mman.h>
+#include <sys/syscall.h>
+], [
+	syscall(SYS_process_madvise, 0, (void *)0, 0, 0, 0);
+], [je_cv_process_madvise])
+  if test "x${je_cv_process_madvise}" = "xyes" ; then
+    AC_DEFINE([JEMALLOC_HAVE_PROCESS_MADVISE], [ ], [ ])
+  fi
 else
   dnl Check for posix_madvise.
   JE_COMPILABLE([posix_madvise], [