pgsql: Try to get some info about Windows can't-reattach-to-shared-memo

Try to get some info about Windows can't-reattach-to-shared-memory errors.

Add some debug printouts focused on the idea that MapViewOfFileEx might
be rounding its virtual memory allocation up more than we expect (and,
in particular, more than VirtualAllocEx does).

Once we've seen what this reports in one of the failures on buildfarm
members dory or jacana, we might revert this ... or perhaps just
decrease the log level.

Discussion: https://postgr.es/m/25495.1524517820@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/63ca350ef9f58d48ac89fd3c68416e319cac0a39

Modified Files
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src/backend/port/win32_shmem.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)