tests: error_hook: Workaround for RX architecture

GCC for RX would crash with an internal compiler error during
DWARF frame generation in `dwarf2out_frame_debug_adjust_cfa()`
when compiling the `trigger_fault_illegal_instruction()`
test function.

This patch adds `__builtin_unreachable()` to help the compiler
reason about control flow, preventing incorrect DWARF CFA
generation.

Signed-off-by: Duy Nguyen <duy.nguyen.xa@renesas.com>

tests/ztest/error_hook/src/main.c

@@ -52,6 +52,15 @@ __no_optimization static void trigger_fault_illegal_instruction(void)
 
 	/* execute an illegal instruction */
 	((void(*)(void))&a)();
+#ifdef CONFIG_RX
+	/*
+	 * Intentionally execute an illegal instruction by calling a NULL pointer.
+	 * Optimization is disabled to avoid GCC internal error during DWARF frame generation.
+	 * __builtin_unreachable() hints to the compiler that control flow never returns here,
+	 * which prevents faulty CFA emission on RX targets.
+	 */
+	__builtin_unreachable();
+#endif
 }
 
 /*