cmd/compile: absorb SNEZ into branch on riscv64

Change-Id: I55fd93843a7fb574a7dd66ebb87fdd96e944d555
Reviewed-on: https://go-review.googlesource.com/c/go/+/221682
Reviewed-by: Cherry Zhang <[email protected]>

Author: 4a6f656c

src/cmd/compile/internal/ssa/gen/RISCV64.rules

@@ -458,6 +458,9 @@
 
 // Optimizations
 
+// Absorb SNEZ into branch.
+(BNE (SNEZ x) yes no) -> (BNE x yes no)
+
 // Fold ADD+MOVDconst into ADDI where possible.
 (ADD (MOVDconst [off]) ptr) && is32Bit(off) -> (ADDI [off] ptr)