Fix RISC-V soft-float _FPU_SETCW for GCC 16 set-but-not-used warnings

[Joseph Myers]

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.

diff --git a/sysdeps/riscv/fpu_control.h b/sysdeps/riscv/fpu_control.h
index 29cf79f2f6..60ea737169 100644
--- a/sysdeps/riscv/fpu_control.h
+++ b/sysdeps/riscv/fpu_control.h
@@ -27,7 +27,7 @@
 # define _FPU_DEFAULT  0x00000000
 typedef unsigned int fpu_control_t;
 # define _FPU_GETCW(cw) (cw) = 0
-# define _FPU_SETCW(cw) do { } while (0)
+# define _FPU_SETCW(cw) (void) (cw)
 extern fpu_control_t __fpu_control;
 
 #else /* __riscv_flen */

-- 
Joseph S. Myers
josmyers@redhat.com