Change prctl() syscall wrapper to take prctl()'s full set of arguments

Change prctl() syscall wrapper to take prctl()'s full set of arguments

The Linux man page documents prctl() as taking upto 5 arguments:

       int prctl(int option, unsigned long arg2, unsigned long arg3,
                 unsigned long arg4, unsigned long arg5);

For example, PR_SET_SECCOMP with SECCOMP_MODE_FILTER takes a third
argument, and so isn't usable without this change.

BUG=none
TEST=none

Committed: https://code.google.com/p/linux-syscall-support/source/detail?r=24

[jln (very slow on Chromium), 2013-08-29 20:04:59]

lgtm

Not an owner, but I think you can TBR Markus.

[Mark Seaborn, 2013-08-31 00:09:01]

Committed patchset #1 manually as r24 (presubmit successful).