Clang Format Update

[David Edmundson]

By the end of tonight there will be a patch in every plasma repo
adding a build target called "clang-format" using the new ECM macros.

Running "make clang-format" or "ninja clang-format" will tidy up all
code in all repos.

I have shipped this target now so that all devs can test the upcoming
changes and provide any feedback or merge any blacklist markers we may
find we want in specific places [1].

THE IMPORTANT BIT

DO NOT merge the resultant tidied files just yet. We shall do so with
a fake author in a week or two.

[1]
int formatted_code;
// clang-format off
    void    unformatted_code  ;
// clang-format on
int formatted_code2;