util/modular: auto-meson-pc-cmp.sh added (merge request)

[tlaronde at kergis.com]

FWIW, I have added to xorg/util/modular, the POSIX.2 sh utility:

auto-meson-pc-cmp.sh 

that allows to compare two directories for pc files, checking that
the same relative pathnames exist in the two dirs and that the same
named files "say" the same things, even if they don't say it the same
way (to not error if autotools is using variables ${variable} while
meson is expending some or defining other variables; the important
thing is that the same configuration leads to the same definitions).

This is to be used by the CI.

BTW: xorgproto doesn't generate the same pc files when using
autogen.sh and meson (default): legacy pc files are generated by
autotools while they are not without the legacy option with meson.

Merge request.
-- 
        Thierry Laronde <tlaronde +AT+ kergis +dot+ com>
                     http://www.kergis.com/
                    http://kertex.kergis.com/
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