[yocto] building output when inherit different bbclasses

[Lu, Lianhao]

Hi guys,

The following list might help someone who wants to figure out what's the difference between the various buildings when inheriting different bbclass(es). 

The normal(default) situation for poky is:

   build = "build system"
   host = target = "set by MACHINE config"

cross.bbclass: 

   build = host = "build system"
   target = "set by MACHINE config"

crosssdk.bbclass: 

   build = host = "build system"
   target = "set by SDKMACHINE config"

native.bbclass:

   build = host = target = "build system"

nativesdk.bbclass:

   build = "build system"
   host = target = "set by SDKMACHINE config"

cross-canadian.bbclass:

   build = "build system"
   host = "set by SDKMACHINE config"
   target = "set by MACHINE config"