[test] Skip ThinLTO cache tests requiring atime setting on NetBSD
[test] Skip ThinLTO cache tests requiring atime setting on NetBSD

Skip the ThinLTO cache tests on NetBSD.  They require 'touch' being
able to alter atime of files, while NetBSD inhibits atime updates
when filesystem is mounted noatime.

Differential Revision: https://reviews.llvm.org/D55273

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@348355 91177308-0d34-0410-b5e6-96231b3b80d8

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