[OpenMP] Update copyright to 2018
[OpenMP] Update copyright to 2018

Better late than never


git-svn-id: f99161ee8ccfe2101cbe1bdda2220bce2ed25485@341703 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp