pgsql: meson: Refactor libpq targets variables

meson: Refactor libpq targets variables

Some of the knowledge of the libpq targets was spread around between
the top-level meson.build and src/interfaces/libpq*. This change
organizes it more like other targets by having a libpq_targets
variable that different subdirectories can add to.

Discussion: /messages/by-id/e8aa97db-872b-4087-b073-f296baae948d@eisentraut.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4bfbbeb679c09c28813d4545bb1f764c3041d475

Modified Files
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meson.build | 12 +++---------
src/interfaces/libpq-oauth/meson.build | 2 ++
src/interfaces/libpq/meson.build | 2 ++
3 files changed, 7 insertions(+), 9 deletions(-)