ARM: GCC < 4.3 has some issues with attribute no return on some functions. Fix so it works for older gccs.

src/arch/arm/isa/templates/basic.isa

@@ -89,5 +89,7 @@ def template BasicExecPanic {{
 Fault execute(%(CPU_exec_context)s *, Trace::InstRecord *) const
 {
         panic("Execute method called when it shouldn't!");
+        // GCC < 4.3 fail to recognize the above panic as no return
+        return NoFault;
 }
 }};