riscv: Build with -mno-relax if linker does not support R_RISCV_ALIGN

It allows build both glibc and tests with lld (Since lld does not
support R_RISCV_ALIGN linker relaxation).

Checked with a build for riscv32-linux-gnu-rv32imafdc-ilp32d and
riscv64-linux-gnu-rv64imafdc-lp64d.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Fangrui Song <maskray@google.com>