[CMake] Refactor add_llvm_tool_symlink for reuse
[CMake] Refactor add_llvm_tool_symlink for reuse

The old implementation of add_llvm_tool_symlink could fail in odd ways when building out of tree. This version solves that problem by not using the LLVM_* variables, and instead reaeding the target's properties.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@288632 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm