Extend 'readonly' and 'readnone' to work on function arguments as well as

Extend 'readonly' and 'readnone' to work on function arguments as well as
functions. Make the function attributes pass add it to known library functions
and when it can deduce it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185735 91177308-0d34-0410-b5e6-96231b3b80d8