pgsql: Remove configure probe for sys/select.h.

Remove configure probe for sys/select.h.

<sys/select.h> is in SUSv3 and every targeted Unix system has it.
Provide an empty header in src/include/port/win32 so that we can
include it unguarded even on Windows.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CA%2BhUKG%2BL_3brvh%3D8e0BW_VfX9h7MtwgN%3DnFHP5o7X2oZucY9dg%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7e50b4e3c52aaa13e86e0560d1382844074c9f1b

Modified Files
--------------
configure                                        | 2 +-
configure.ac                                     | 1 -
doc/src/sgml/libpq.sgml                          | 4 +---
src/backend/libpq/auth.c                         | 4 +---
src/backend/postmaster/postmaster.c              | 5 +----
src/backend/tcop/postgres.c                      | 4 +---
src/bin/pg_basebackup/pg_basebackup.c            | 4 +---
src/bin/pg_basebackup/pg_recvlogical.c           | 4 +---
src/bin/pg_basebackup/receivelog.c               | 4 +---
src/bin/pg_dump/parallel.c                       | 4 +---
src/bin/pgbench/pgbench.c                        | 2 --
src/fe_utils/parallel_slot.c                     | 2 --
src/include/pg_config.h.in                       | 3 ---
src/include/port/win32/sys/select.h              | 3 +++
src/interfaces/libpq/fe-misc.c                   | 4 +---
src/port/pgsleep.c                               | 4 +---
src/test/examples/testlibpq2.c                   | 4 +---
src/test/isolation/isolationtester.c             | 4 +---
src/test/modules/libpq_pipeline/libpq_pipeline.c | 4 +---
src/tools/msvc/Solution.pm                       | 1 -
20 files changed, 17 insertions(+), 50 deletions(-)