pgsql: Fix the initialization of atomic variables introduced by the

Fix the initialization of atomic variables introduced by the
group clearing mechanism.

Commits 0e141c0fbb and baaf272ac9 introduced initialization of atomic
variables in InitProcess which means that it's not safe to look at those
for backends that aren't currently in use. Fix that by initializing them
during postmaster startup.

Reported-by: Andres Freund
Author: Amit Kapila
Backpatch-through: 9.6
Discussion: https://postgr.es/m/20181027104138.qmbbelopvy7cw2qv@alap3.anarazel.de

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/d4d9f21b64d4290cc6695bcd93a8e4c5fc16badf

Modified Files
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src/backend/storage/lmgr/proc.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)