[compiler-rt][XRay] Only add xray dependency if XRay is built and is available for the platform
[compiler-rt][XRay] Only add xray dependency if XRay is built and is available for the platform

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@277983 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt