pgsql: Disable some C++ warnings in MSVC

Disable some C++ warnings in MSVC

Flexible array members, as used in many PostgreSQL header files, are
not a C++ feature. MSVC warns about these. Disable the
warning. (GCC and Clang accept them, but they would warn in -pedantic
mode.)

Reviewed-by: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion: /messages/by-id/CAGECzQR21OnnKiZO_1rLWO0-16kg1JBxnVq-wymYW0-_1cUNtg@mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/82a7cbea747c465eee8449587be2d6cc47af82fe

Modified Files
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meson.build | 3 +++
1 file changed, 3 insertions(+)