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

@@ -159,12 +159,23 @@
         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 16-byte aligned stack pointer */
+        subl    $4,%esp         /* a properly aligned stack pointer */
         pushl   %edx
         leal    12(%ebp),%edx   /* argv */
         movl    %edx,___Argv
         pushl   %edx
         pushl   %eax            /* argc */