Fix Clang error when disabling MOP FUSION

When using 'make ENABLE_MOP_FUSION=0 CC=clang', the following error is
observed:
src/emulate.c:695:20: error: unused function 'remove_next_nth_ir' [-Werror,-Wunused-function]
  695 | static inline void remove_next_nth_ir(const riscv_t *rv,
	  |                    ^~~~~~~~~~~~~~~~~~
1 error generated.

Fix this by guarding the remove_next_nth_ir function definition with
RV32_HAS(MOP_FUSION) macro. This ensures the function is only defined
when the MOP_FUSION is enabled.

Author: eleanorLYJ

src/emulate.c

@@ -692,6 +692,7 @@ static void block_translate(riscv_t *rv, block_t *block)
         remove_next_nth_ir(rv, ir, block, count - 1);             \
     }
 
+#if RV32_HAS(MOP_FUSION)
 static inline void remove_next_nth_ir(const riscv_t *rv,
                                       rv_insn_t *ir,
                                       block_t *block,
@@ -706,6 +707,7 @@ static inline void remove_next_nth_ir(const riscv_t *rv,
         block->ir_tail = ir;
     block->n_insn -= n;
 }
+#endif
 
 #if RV32_HAS(MOP_FUSION)
 /* Check if instructions in a block match a specific pattern. If they do,