Update `.clang-format` with configuration to make the 6.0 format as
close as possible to what 3.8 produced before.  Then revise the style:

* Indent preprocessor directives (a feature new since 3.8)
* Add a newline and indentation before inheritance `:` and `,`

Fix the path to the script within this source tree in example commands.

Change-Id: Iee85cf12b2cf49eea7959685fe9bec223f7c1ff2

List all sources in version control and filter out those that we should
not format for various reasons.  Then run the clang-format tool to do an
in-place update.

Change-Id: If6d24b3b2e2de1b8e66f7fc2a713d2fd1d579f3d