pdh: Add a stub implementation of PdhSetDefaultRealTimeDataSource.
diff --git a/dlls/pdh/pdh_main.c b/dlls/pdh/pdh_main.c
index 7f08c92..fd6deba 100644
--- a/dlls/pdh/pdh_main.c
+++ b/dlls/pdh/pdh_main.c
@@ -1211,3 +1211,12 @@
 
     return PDH_NOT_IMPLEMENTED;
 }
+
+/***********************************************************************
+ *              PdhSetDefaultRealTimeDataSource   (PDH.@)
+ */
+PDH_STATUS WINAPI PdhSetDefaultRealTimeDataSource( DWORD source )
+{
+    FIXME("%u\n", source);
+    return ERROR_SUCCESS;
+}