Thanks to Ronaldo Nunez in youtube (Intro to OpenWRT by Ronaldo Nunez), and OpenWRT community for supporting

Install dependency packages if compilation fails, example: gawk, python2 etc.

openwrt compilation process as below step by step,

$git clone https://github.com/openwrt/openwrt.git -b openwrt-19.07 $cd openwrt/ $scripts/feeds update $sudo scripts/feeds install -a $sudo make menuconfig $sudo make download $sudo su $export FORCE_UNSAFE_CONFIGURE=1 $make -j16 V=s