[NFC] [DebugCounter] warn if --debug-counter is unused in NDEBUG (#143057)

Co-authored-by: Nikita Popov <[email protected]>

Author: fmayer

llvm/lib/Support/DebugCounter.cpp

@@ -172,6 +172,11 @@ DebugCounter &DebugCounter::instance() {
 void DebugCounter::push_back(const std::string &Val) {
   if (Val.empty())
     return;
+#ifdef NDEBUG
+  // isCountingEnabled is hardcoded to false in NDEBUG.
+  errs() << "Requested --debug-counter in LLVM build without assertions. This "
+            "is a no-op.\n";
+#endif
 
   // The strings should come in as counter=chunk_list
   auto CounterPair = StringRef(Val).split('=');