Build with crosstool-ng
CT_CONFIG_VERSION="3"
CT_ARCH_XTENSA=y
CT_XTENSA_CUSTOM=y
CT_OVERLAY_NAME="hifi4"
CT_OVERLAY_LOCATION="/root/xtensa-hifi4-dsp"
CT_TARGET_VENDOR="hifi4"
CT_NEWLIB_SRC_DEVEL=y
CT_NEWLIB_DEVEL_URL="https://github.com/espressif/newlib-esp32/"
CT_GCC_V_10=y
CT_CC_LANG_CXX=y