[Clang][RISCV] Forward --no-relax option to linker for RISC-V (#76432)

In the case of -mno-relax option. Otherwise, we cannot prevent
relaxation if we split compilation and linking using Clang driver.

One can consider the following use case:

clang [...] -c -o myobject.o (just compile)
clang [...] myobject.o -o myobject.elf -mno-relax (linking)

In this case, myobject.elf will be relaxed, the -mno-relax will be
silently ignored.