Supporting huge pages on Windows

Hello,

The attached patch implements huge_pages on Windows. I'll add this to the CommitFest.

The performance improvement was about 2% with the following select-only pgbench. The scaling factor is 200, where the database size is roughly 3GB. I ran the benchmark on my Windows 10 PC with 6 CPU cores and 16GB of RAM.

　　pgbench -c18 -j6 -T60 -S bench

Before running pgbench, I used pg_prewarm to cache all pgbench tables and indexes (excluding the history table) in the 4GB shared buffers. The averages of running pgbench three times are:

huge_pages=off: 70412 tps
huge_pages=on : 72100 tps

The purpose of pg_ctl.c modification is to retain "Lock pages in memory" Windows user right in postgres. That user right is necessary for the large-page support. The current pg_ctl removes all privileges when spawning postgres, which is overkill. The system administrator should be able to assign appropriate privileges to the PostgreSQL service account.

Credit: This patch is based on Thomas Munro's one.

Regards
Takayuki Tsunakawa