Changes to alternate platform name

[sirzooro]

I have two requests:

• Please print alternate platform name in event log, now it is not obvious if BOINC client started using value configured in cc_config.xml using <alt_platform> or not;
• I have Odroid C2 which uses platform aarch64-unknown-linux-gnu, and I have tag <alt_platform>arm-unknown-linux-gnueabihf</alt_platform> in my cc_config.xml. Now I would like to add second alternative platform <alt_platform>armv6l-unknown-linux-gnueabihf</alt_platform>. Client configuration page does not say if it is possible to use this tag multiple times, so I assume that this would not work (I did not try to to this). Please either add such feature to BOINC or update that page.

[davidpanderson]

It is possible to have multiple alt platforms. I changed the doc to say so.
Also I added prints of alt platforms in the event log.

[sirzooro]

Thanks!