Improve error reporting for unsupported effective_io_concurrency setting.
Give a specific error complaining about lack of posix_fadvise() when
someone tries to set effective_io_concurrency > 0 on platforms
without that.
This probably isn't worth extensive back-patching, but I (tgl) felt
cramming it into v11 was reasonable.
James Robinson
Discussion: https://postgr.es/m/
153771876450.14994.
560017943128223619@wrigleys.postgresql.org
Discussion: https://postgr.es/m/
A3942987-5BC7-4F05-B54D-
2A0EC2914B33@jlr-photo.com