cyrus-imapd build dependencies

[Patrick Goetz]

This page on compiling cyrus-imapd:

   https://www.cyrusimap.org/imap/developer/compiling.html

shows a number of build dependencies; however I was just able to compile 
cyrus-imapd without these installed:

    gperf
    libbsd


Are these actually necessary?

Later in the page, under "Alternate database formats" it shows the 
configure flags to use in order to use mysql/mariadb as a backend for 
cyrus databases.  I think this is needed if one plans to use virtual 
domains, but I couldn't get a confirmation on this.  In any case, the 
configure options are given as

  --with-mysql, --with-mysql-incdir, --with-mysql-libdir

with no clear indication of what each of these does.  For example, is 
the --with-mysql all inclusive, or does one need to set all 3?

Finally a couple of items in the "Other" category are a real head 
scratcher.  For example, what is the purpose of net-snmp?

libnghttp2 is listed as needed for "HTTP/2 support for httpd" -- what's 
using httpd?  Is this to faciliate CalDAV/CardDAV?