[CMake]  NFC. Add intrinsics_gen target to CMake Exports
[CMake]  NFC. Add intrinsics_gen target to CMake Exports

By creating a dummy of this target in LLVMConfig.cmake, projects that can build against out-of-tree LLVM can freely depend on the target without needing to have conditionals for if LLVM is in-tree or out-of-tree.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@309389 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm