[patch] Build pgoutput with MSVC

Hello,

I tried logical replication on Windows, but it failed like this:

postgres=# create subscription mysub connection 'host=localhost
port=5433 user=tuna dbname=postgres' publication mypub with (nocopy
data);
NOTICE: synchronized table states
ERROR: could not create replication slot "mysub": ERROR: could not
access file "pgoutput": No such file or directory
postgres=#

The pgoutput is not built with MSVC. The attached patch fixes this.
I confirmed that a few INSERTs were replicated correctly.

Should I add this matter in the PostgreSQL 10 Open Items page?

Regards
MauMau