pgsql: Fix handling Inf and Nan values in GiST pairing heap comparator

Fix handling Inf and Nan values in GiST pairing heap comparator

Previously plain float comparison was used in GiST pairing heap.  Such
comparison doesn't provide proper ordering for value sets containing Inf and Nan
values.  This commit fixes that by usage of float8_cmp_internal().  Note, there
is remaining problem with NULL distances, which are represented as Inf in
pairing heap.  It would be fixes in subsequent commit.

Backpatch to all supported versions.

Reported-by: Andrey Borodin
Discussion: https://postgr.es/m/CAPpHfdsNvNdA0DBS%2BwMpFrgwT6C3-q50sFVGLSiuWnV3FqOJuQ%40mail.gmail.com
Author: Alexander Korotkov
Reviewed-by: Heikki Linnakangas
Backpatch-through: 9.4

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/749b04d1d8b8ad63d365b8f6ad9d70843f3c1239

Modified Files
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src/backend/access/gist/gistscan.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)