qmake: Add support for arm64 hosts on Windows

Pick-to: 6.8
Change-Id: I0096300fce870ef4411b071f074588a6420188e0
Reviewed-by:  Alexey Edelev <alexey.edelev@qt.io>
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

qmake/library/qmakeevaluator.cpp

@@ -1046,6 +1046,11 @@ void QMakeEvaluator::loadDefaults()
     case PROCESSOR_ARCHITECTURE_AMD64:
         archStr = ProString("x86_64");
         break;
+# endif
+# ifdef PROCESSOR_ARCHITECTURE_ARM64
+    case PROCESSOR_ARCHITECTURE_ARM64:
+        archStr = ProString("arm64");
+        break;
 # endif
     case PROCESSOR_ARCHITECTURE_INTEL:
         archStr = ProString("x86");