pgsql: Fix searchpath for modern Perl for genbki.pl

Fix searchpath for modern Perl for genbki.pl

This was fixed for MSVC tools by commit 1df92eeafefac4, but per
buildfarm member bowerbird genbki.pl needs the same treatment.

Backpatch to all live branches.

Branch
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REL9_5_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a82ca6ffb6de124cf3ffdf32e401ec2d35eca4de

Modified Files
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src/backend/catalog/genbki.pl | 4 ++++
1 file changed, 4 insertions(+)