classes/populate_sdk_ext: support setting vars from environment at build time
When running bitbake you may pass in values of variables from the
external environment (making use of BB_ENV_EXTRAWHITE), and you may
choose to do this when building the extensible SDK, for example:
You would naturally expect those settings to be reflected in the
extensible SDK itself; however they were not, since we were only
considering local.conf and auto.conf. Check the variables mentioned in
BB_ENV_EXTRAWHITE to see if any are different than the values set in
local.conf/auto.conf and add lines setting them in the SDK's local.conf
if so.
Fixes [YOCTO #9339].
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
