pgsql: Turn off deprecated bison warnings under MSVC

Turn off deprecated bison warnings under MSVC

These are disabled by the configure code, so this is just fixing an
inconsistency in the MSVC code.

Backpatch to all live branches.

Branch
------
REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/3163349fd7fe0115b021bfa1fbe4990143957814

Modified Files
--------------
src/tools/msvc/pgbison.pl | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)