disas/riscv: Make rv_op_illegal a shared enum value

The enum value 'rv_op_illegal' does not represent an
instruction, but is a catch-all value in case we have
no match in the decoder. Let's make the value a shared
one, so that other compile units can reuse it.

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
Message-Id: <20230612111034.3955227-5-christoph.muellner@vrull.eu>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

disas/riscv.c

@@ -23,7 +23,7 @@
 #include "disas/riscv.h"
 
 typedef enum {
-    rv_op_illegal = 0,
+    /* 0 is reserved for rv_op_illegal. */
     rv_op_lui = 1,
     rv_op_auipc = 2,
     rv_op_jal = 3,

disas/riscv.h

@@ -191,6 +191,10 @@ typedef struct {
     const rvc_constraint *constraints;
 } rv_comp_data;
 
+enum {
+    rv_op_illegal = 0
+};
+
 enum {
     rvcd_imm_nz = 0x1
 };