Disable a few clang-tidy checks by default.

The goal is to be able to run clang-tidy on LLVM files without further
configuration for now. Once llvm.org/PR19306 is addressed, we can add a
configuration file instead and choose other defaults.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@205407 91177308-0d34-0410-b5e6-96231b3b80d8
Fix regex bug in clang-tidy.

Also make tests slightly less dependent on default flags. Once we have
implemented configuration file support, we might want to store the
clang-tidy configuration for the tests there.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@205408 91177308-0d34-0410-b5e6-96231b3b80d8