[DOCS] Building extension on Windows

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/9.6/static/xfunc-c.html
Description:

Does the macros PG_FUNCTION_INFO_V1 work properly on windows?

Using visual studio 2013 on windows os,the full function definition must
look like that:

PGDLLEXPORT Datum Test(PG_FUNCTION_ARGS);

PG_FUNCTION_INFO_V1(Test);

Datum Test(PG_FUNCTION_ARGS){
}

And some specific flags must be set on the project settings.