Add .clang-format without column limit to subdirectory tests/.

A column limit in the test folder can lead to trouble as the RUN, CHECK,
etc. comments can potentially be broken over multiple lines changing
their meaning. Without column limit, clang-format will simply keep the
test author's line breaks.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194248 91177308-0d34-0410-b5e6-96231b3b80d8