The soft-float RISC-V definition of _FPU_SETCW results in a
-Werror=unused-but-set-variable= build failure with GCC mainline (in
math/setfpucw.c) because it does not use the dummy cw variable.
Change it to (void) (cw) as on other architectures to avoid this build
failure.
Tested with build-many-glibcs.py (compilers) for
riscv64-linux-gnu-rv64imac-lp64, which previously failed.
Reviewed-by: Sam James <sam@gentoo.org>
273f80374a