Disable data formatter tests on Windows.

clang does not yet support MS-ABI record layout for externally-sourced
ASTs.  As a result, attempting to format something that requires data
layout results in undefined behavior in clang, in this case an assert.

http://llvm.org/pr21800 tracks fixing this on the clang side.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@223868 91177308-0d34-0410-b5e6-96231b3b80d8