fix multilib support and rework --with-extra-multilib-test#1395

ewlu wants to merge 1 commit intoriscv-collab:masterriscv-collab/riscv-gnu-toolchain:masterfrom

patrick-rivos:change-with-extra-multilib-testpatrick-rivos/riscv-gnu-toolchain:change-with-extra-multilib-testCopy head branch name to clipboard