Tools/MMapsGenerator: Use system supported threads instead of hardcoded amount (#19255)

- Use unsigned int for thread count
- Use std::thread::hardware_concurrency() to try estimate available threads instead of hardcoded 3 threads by default
- Print thread count always regardless of using --threads switch or not

src/tools/mmaps_generator/MapBuilder.cpp

@@ -190,9 +190,11 @@ namespace MMAP
         }
     }
 
-    void MapBuilder::buildAllMaps(int threads)
+    void MapBuilder::buildAllMaps(unsigned int threads)
     {
-        for (int i = 0; i < threads; ++i)
+        printf("Using %u threads to extract mmaps\n", threads);
+
+        for (unsigned int i = 0; i < threads; ++i)
         {
             _workerThreads.push_back(std::thread(&MapBuilder::WorkerThread, this));
         }