When providing a block literal as a code completion for a

When providing a block literal as a code completion for a
function/method argument, include the parameter name and always
include parentheses (even for zero-parameter blocks). Otherwise, the
block literal placeholder '^' can look very weird.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@115444 91177308-0d34-0410-b5e6-96231b3b80d8