pgsql: Doc: Update example symptom of systemd misconfiguration.

Doc: Update example symptom of systemd misconfiguration.

In PostgreSQL 10, we stopped using System V semaphores on Linux
systems.  Update the example we give of an error message from a
misconfigured system to show what people are most likely to see these
days.

Back-patch to 10, where PREFERRED_SEMAPHORES=UNNAMED_POSIX arrived.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CA%2BhUKGLmJUSwybaPQv39rB8ABpqJq84im2UjZvyUY4feYhpWMw%40mail.gmail.com

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/682c28baf9251a1406bfcad15243c8fca6594742

Modified Files
--------------
doc/src/sgml/runtime.sgml | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)