6507 i386 makecontext(3c) needs to 16-byte align the stack

*** 159,170 ****
          testl   %edx, %edx              /* check if _enviorn==0 */
          jne     1f                      /* fixed bug 4203802 */
          leal    16(%ebp,%eax,4),%edx    /* envp */
          movl    %edx,_environ           /* copy to _environ */
  1:
          andl    $-16,%esp       /* make main() and exit() be called with */
!         subl    $4,%esp         /* a 16-byte aligned stack pointer */
          pushl   %edx
          leal    12(%ebp),%edx   /* argv */
          movl    %edx,___Argv
          pushl   %edx
          pushl   %eax            /* argc */
--- 159,181 ----
          testl   %edx, %edx              /* check if _enviorn==0 */
          jne     1f                      /* fixed bug 4203802 */
          leal    16(%ebp,%eax,4),%edx    /* envp */
          movl    %edx,_environ           /* copy to _environ */
  1:
+         /*
+          * The stack needs to be 16-byte aligned with a 4-byte bias.  See
+          * comment in lib/libc/i386/gen/makectxt.c.
+          *
+          * Note: If you change it, you need to change it in the following
+          * files as well:
+          *
+          *  - lib/libc/i386/threads/machdep.c
+          *  - lib/libc/i386/gen/makectxt.c
+          *  - lib/common/i386/crti.s
+          */
          andl    $-16,%esp       /* make main() and exit() be called with */
!         subl    $4,%esp         /* a properly aligned stack pointer */
          pushl   %edx
          leal    12(%ebp),%edx   /* argv */
          movl    %edx,___Argv
          pushl   %edx
          pushl   %eax            /* argc */