[PATCH v2] sim: mark local insn var as unused [PR sim/31181]

Some insns are fully decoded by the time they execute here, and don't
need to extract any more fields.  This leads to the local insn var
being unused which triggers compiler warnings.  Mark it as unused so
we don't require ports to stub it themselves.

Bug: https://sourceware.org/PR31181
---
v2
- move decl to after the var name, not before the type

 sim-decode.scm | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/sim-decode.scm b/sim-decode.scm
index 19c0d4677424..5284da074166 100644
--- a/sim-decode.scm
+++ b/sim-decode.scm
@@ -436,7 +436,13 @@ void
    "    const IDESC *idesc = &" IDESC-TABLE-VAR "[itype];\n"
    (if (> (length (sfmt-iflds sfmt)) 0)
        (string-append
-	"    CGEN_INSN_WORD insn = "
+	"    CGEN_INSN_WORD insn"
+	; Some insns are fully decoded by the time they get here, so they won't
+	; access the insn variable.  Mark it as unused to avoid warnings.
+	(if (adata-integral-insn? CURRENT-ARCH)
+	    ""
+	    " ATTRIBUTE_UNUSED")
+	" = "
 	(if (adata-integral-insn? CURRENT-ARCH)
 	    "entire_insn;\n"
 	    "base_insn;\n"))
-- 
2.43.0