Add 3.4.2 release directory with new naming convention.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/tags/RELEASE_342@213538 91177308-0d34-0410-b5e6-96231b3b80d8
tree: 4b825dc642cb6eb9a060e54bf8d69288fbee4904

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