PR15290: 'this' is not permitted in the declaration of a friend function,
therefore references to members should not be transformed into implicit uses of
'this'. Patch by Ismail Pazarbasi!


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177134 91177308-0d34-0410-b5e6-96231b3b80d8