clang-format: Fix parsing and indenting lambdas.

Before:
  void f() {
    other(x.begin(), x.end(), //
                         [&](int, int) { return 1; });
  }

After:
  void f() {
    other(x.begin(), x.end(), //
          [&](int, int) { return 1; });
  }

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190039 91177308-0d34-0410-b5e6-96231b3b80d8
Support suppressing unused arguments warnings as a core option so that
it works in the CL flavor driver.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190040 91177308-0d34-0410-b5e6-96231b3b80d8
Address post-commit review comments from r190038.

Mostly additional comments :-).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190042 91177308-0d34-0410-b5e6-96231b3b80d8