To work with the board which tool chain is advised? Newlib or glibc?

newlib. We're not booting a Linux system here. . . Newlib is what you use with simple embedded microcontroller systems.

The efabless website directs to a risc v site. There both the options are listed. It was never said that glibc should not be used. And its not about booting linux on riscv, its about choosing cross compiler on a linux destop. Glibc is just a cross compiler, its not a linux distribution.