Update to build against the latest revision of linux_syscall_support.h

Update to build against the latest revision of linux_syscall_support.h

The prctl() calls must be updated following this LSS change:
https://code.google.com/p/linux-syscall-support/source/detail?r=24

BUG=none
TEST=build

Committed: https://code.google.com/p/google-breakpad/source/detail?r=1210

[mseaborn]

My change also updates the LSS revision as follows, though gcl/Rietveld don't
show that:

$ svn diff src/third_party/

Property changes on: src/third_party
___________________________________________________________________
Modified: svn:externals
   - lss -r12 http://linux-syscall-support.googlecode.com/svn/trunk/lss
glog -r97 http://google-glog.googlecode.com/svn/trunk

   + lss -r24 http://linux-syscall-support.googlecode.com/svn/trunk/lss
glog -r97 http://google-glog.googlecode.com/svn/trunk

[Mark Mentovai]

LGTM

[mseaborn]

Committed patchset #1 manually as r1210 (presubmit successful).