At some point we lost the ability to record the contents of the SDK in buildhistory - the function isn't being added to SDK_POSTPROCESS_COMMAND and thus the data is never written out.
Fixed merged to master: http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=ea0abcdd17debeda43307cebab1ebf8bfe272e6a
SDK build info is recorded: verified on master: f8185ff9f8ac697733b41f023cb3a4b98b2f823f