Write transform results to disk only once
    
Instead of writing the result of each transform to disk for every
transform, write the results to buffers in memory and pass those buffers
to the next transform as input. Only write the buffers to disk if the
final syntax check passes.

Reviewers: klimek


git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@172657 91177308-0d34-0410-b5e6-96231b3b80d8