pgsql: Add port/ replacement for strsep()

Add port/ replacement for strsep()

from OpenBSD, similar to strlcat, strlcpy

There are currently no uses, but some will be added soon.

Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-by: David Steele <david@pgmasters.net>
Discussion: /messages/by-id/79692bf9-17d3-41e6-b9c9-fc8c3944222a@eisentraut.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/683be87fbba02b086cc05789fcbdc289120d1065

Modified Files
--------------
configure | 23 ++++++++++++++
configure.ac | 3 +-
meson.build | 2 ++
src/include/pg_config.h.in | 7 +++++
src/include/port.h | 4 +++
src/port/meson.build | 1 +
src/port/strsep.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++
7 files changed, 116 insertions(+), 1 deletion(-)