pgsql: meson: Make room for C++-only warning flags for MSVC

meson: Make room for C++-only warning flags for MSVC

Refactor the MSVC warning option handling to have a list of common
flags and lists of flags specific to C and C++.

Reviewed-by: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion:
https://www.postgresql.org/message-id/flat/CAGECzQR21OnnKiZO_1rLWO0-16kg1JBxnVq-wymYW0-_1cUNtg%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4c83f1253593ef46a0a190afb8ecead21f483196

Modified Files
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meson.build | 31 +++++++++++++++++++++++--------
1 file changed, 23 insertions(+), 8 deletions(-)