Merge request for auto-meson-pc-cmp.sh + Meson and CI for xcbproto

[tlaronde at kergis.com]

I have completed the documentation about the steps for adding Meson
and CI to xcbproto:

https://notes.kergis.com/x11_building.html

(I tried to make explanations clear and work for a CSS presenting
things clearer too; I'd like review about the document for feedback.
TIA)

The problem is with the script:

auto-meson-pc-cmp.sh

that I had written (it is in xorg/util/modular) to compare
semantically pc files in two directories: for safety reasons,
I was forcing the use of fully qualified directories as arguments. But
in the CI, the directories are passed relative.

So the pipeline fails when comparing the pc files because of the
arguments passed (not fully qualified).

So I have modified the script (in tlaronde/modular) and need it to be
updated in the master.

TIA
-- 
        Thierry Laronde <tlaronde +AT+ kergis +dot+ com>
                     http://www.kergis.com/
                    http://kertex.kergis.com/
                     http://nunc-et-hic.fr/
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