Consolidate single void paramter checking

Also correct argument/parameter terminology.

No change in functionality.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208498 91177308-0d34-0410-b5e6-96231b3b80d8
Parameter/argument terminology fixes

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208499 91177308-0d34-0410-b5e6-96231b3b80d8