[libunwind] Silence a warning about an unused variable, if building without asserts

[mstorsjo]

Superseded by D107835.

libunwind/src/Unwind-seh.cpp

if (_LIBUNWIND_TRACING_UNWINDING) {
                                &offset) != UNW_ESUCCESS) ||
           (frameInfo.start_ip + offset > frameInfo.end_ip))
         functionName = ".anonymous.";
       _LIBUNWIND_TRACE_UNWINDING(
           "unwind_phase2_forced(ex_ojb=%p): start_ip=0x%" PRIx64
           ", func=%s, lsda=0x%" PRIx64 ", personality=0x%" PRIx64,
           (void *)exception_object, frameInfo.start_ip, functionName,
           frameInfo.lsda, frameInfo.handler);
+      (void)functionName;
     }
 
     // Call stop function at each frame.
     _Unwind_Action action =
         (_Unwind_Action)(_UA_FORCE_UNWIND | _UA_CLEANUP_PHASE);
     _Unwind_Reason_Code stopResult =
         (*stop)(1, action, exception_object->exception_class, exception_object,
                 (struct _Unwind_Context *)(&cursor2), stop_parameter);