add Linux syscall wrappers and ThreadLister to sanitizer_common

ThreadLister is a Linux-specific class for obtaining the thread IDs of a process from procfs (/proc/<pid>/task/). It will be used by leak checking code.
Also add several syscall wrappers which will be required by the same code that uses ThreadLister, but are not used in ThreadLister itself.
Patch by Sergey Matveev


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@176179 91177308-0d34-0410-b5e6-96231b3b80d8