[dsymutil] Do not create temporary files in -no-output mode.

[dsymutil] Do not create temporary files in -no-output mode.

The files were never written to and then deleted, but they were created
nonetheless. To prevent that, create a wrapper around the 2 variants of
createUniqueFile and use the one that only does an access(Exists) call
to check for name unicity in -no-output mode.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244172 91177308-0d34-0410-b5e6-96231b3b80d8