Add empty release notes for 3.4.
Add empty release notes for 3.4.

The idea is that docs/ReleaseNotes.rst is 3.3 and will be copied to the
branch by the release manager just before creating the release
candidates.

This ReleaseNotes_34.rst will then be moved over ReleaseNotes.rst after
the 3.3 release.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@181349 91177308-0d34-0410-b5e6-96231b3b80d8

chubbymaggie/asap,apple/swift-llvm,chubbymaggie/asap,GPUOpen-Drivers/llvm,chubbymaggie/asap,dslab-epfl/asap,apple/swift-llvm,dslab-epfl/asap,dslab-epfl/asap,llvm-mirror/llvm,chubbymaggie/asap,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,chubbymaggie/asap,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,dslab-epfl/asap,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,chubbymaggie/asap,dslab-epfl/asap,dslab-epfl/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm