pgsql: Add some test coverage for ecpg's "long long" support.

Add some test coverage for ecpg's "long long" support.

This will only actually exercise the "long long" code paths on platforms
where "long" is 32 bits --- otherwise, the SQL bigint type maps to
plain "long", and we will test that code path instead. But that's
probably sufficient coverage, and anyway we weren't testing either
code path before.

Dang Minh Huong, tweaked a bit by me

Discussion: https://postgr.es/m/151935568942.1461.14623890240535309745@wrigleys.postgresql.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/dbccdd375b41618ca4ee3d1ea7109ab7f95d0865

Modified Files
--------------
src/interfaces/ecpg/test/expected/sql-sqlda.c | 140 ++++-----
src/interfaces/ecpg/test/expected/sql-sqlda.stderr | 326 +++++++++++----------
src/interfaces/ecpg/test/expected/sql-sqlda.stdout | 8 +
src/interfaces/ecpg/test/sql/sqlda.pgc | 18 +-
4 files changed, 273 insertions(+), 219 deletions(-)