参考：http://arago-project.org/wiki/index.php/Setting_Up_Build_Environment#Point_to_the_toolchain_to_use
1）下载，安装Linaro toolchain
2）设置BBLAYERS
3）设置bitbake 环境变量，修改
MACHINE?=”am57xx-evm”
TOOLCHAIN_PATH?=”/home/john/gcc-linaro-7.2.1-2017.11-x86_64_arm-linux-gnueabihf”
bblayes.conf文件的内容
This template file was created by taking the oe-core/meta/conf/bblayers.conf
file and removing the BBLAYERS section at the end.
LAYER_CONF_VERSION is increased each time build/conf/bblayers.conf
changes incompatibly
LCONF_VERSION = “7”
BBPATH = “${TOPDIR}”
BBFILES ?= “”
Layers configured by oe-core-setup script
BBLAYERS += ” \
/home/john/tisdk/sources/meta-arago/meta-arago-distro \
/home/john/tisdk/sources/meta-arago/meta-arago-extras \
/home/john/tisdk/sources/meta-browser \
/home/john/tisdk/sources/meta-qt5 \
/home/john/tisdk/sources/meta-openembedded/meta-networking \
/home/john/tisdk/sources/meta-openembedded/meta-python \
/home/john/tisdk/sources/meta-openembedded/meta-oe \
/home/john/tisdk/sources/meta-openembedded/meta-gnome \
/home/john/tisdk/sources/meta-ti \
/home/john/tisdk/sources/meta-linaro/meta-linaro-toolchain \
/home/john/tisdk/sources/meta-linaro/meta-optee \
/home/john/tisdk/sources/oe-core/meta \
“
