The exception-declaration for a function-try-block cannot redeclare a
function parameter. One of our existing test cases was XFAILed because
of this. This fixes the issue and un-XFAILs the test.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210026 91177308-0d34-0410-b5e6-96231b3b80d8