pgsql: Bump minimum version of Flex to 2.5.35

Bump minimum version of Flex to 2.5.35

Since the retirement of some older buildfarm members, the oldest Flex
that gets regular testing is 2.5.35.

Reviewed by Andres Freund
Discussion: https://www.postgresql.org/message-id/1097762.1662145681@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8b878bffa8d8ac7e13508025c3ca5e6101e3a5e8

Modified Files
--------------
config/programs.m4                | 10 ++++------
configure                         |  6 +++---
doc/src/sgml/install-windows.sgml |  2 +-
doc/src/sgml/installation.sgml    |  2 +-
src/backend/utils/misc/guc-file.l |  4 ++--
src/tools/msvc/pgflex.pl          |  2 +-
6 files changed, 12 insertions(+), 14 deletions(-)