Implement DR577

DR18 previously forebode typedefs to be used as parameter types if they
were of type 'void'.  DR577 allows 'void' to be used as a function
parameter type regardless from where it came.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201631 91177308-0d34-0410-b5e6-96231b3b80d8