pgsql: Hmm, seems a lot of the buildfarm is running versions of awk that

Log Message:
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Hmm, seems a lot of the buildfarm is running versions of awk that
don't have gensub(). Use sub() instead, tedious though it be.

Modified Files:
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pgsql/src/backend/catalog:
genbki.sh (r1.47 -> r1.48)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/genbki.sh?r1=1.47&r2=1.48)