[lit] Fix problem in how Python versions open files with different encodings
[lit] Fix problem in how Python versions open files with different encodings

Reapply D43165 which was reverted because of different versions of python failing. 
The one line fix for the different python versions was commited at the same time
that D43165 was reverted. If this change is giving you issues then get in touch
with your python version and we will fix it. 


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@329022 91177308-0d34-0410-b5e6-96231b3b80d8

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