pgsql: Remove select(2) backed latch implementation.

Remove select(2) backed latch implementation.

poll(2) is required by Single Unix Spec v2, the usual baseline for
postgres (leaving windows aside). There's not been any buildfarm
animals without poll(2) for a long while, leaving the select(2)
implementation to be largely untested.

On windows, including mingw, poll() is not available, but we have a
special case implementation for windows anyway.

Author: Andres Freund
Discussion: https://postgr.es/m/20170420003611.7r2sdvehesdyiz2i@alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/61c21ddad03dda1f92a05a723cf449087d80ec08

Modified Files
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src/backend/storage/ipc/latch.c | 221 +++++-----------------------------------
1 file changed, 28 insertions(+), 193 deletions(-)