pgsql: Zero initialize uses of instr_time about to trigger compiler war

Zero initialize uses of instr_time about to trigger compiler warnings

These are all not necessary from a correctness POV. However, in the near
future instr_time will be simplified to an int64, at which point gcc would
otherwise start to warn about the changed places.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: /messages/by-id/20230116023639.rn36vf6ajqmfciua@awork3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/25b2aba0c3a501e2af9579f1b629f155544935db

Modified Files
--------------
src/backend/access/transam/xlog.c | 4 ++++
src/backend/storage/buffer/bufmgr.c | 4 ++++
src/backend/storage/file/buffile.c | 4 ++++
src/backend/storage/ipc/latch.c | 2 ++
src/bin/psql/common.c | 6 ++++++
5 files changed, 20 insertions(+)