build-setup: Inject environments to local.conf

Add ENV_LOCAL_CONF so that the environment could be injected into local.conf
of the openbmc build.

Typically the ENV_LOCAL_CONF could be defined as a variable containing
key=value with newlines, e.g.

    export ENV_LOCAL_CONF="key1=\"${value1}\"
    key2=\"${value2}\""

So that the below texts are appended into local.conf for the build:

    key1="value1"
    key2="value2"

Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: I4cffece334b8257e3a82a5fae7cf3813d1f489eb
1 file changed