threading: decorate Vulkan commands with VKAPI_ATTR
diff --git a/genvk.py b/genvk.py
index 7ea70c2..993477c 100755
--- a/genvk.py
+++ b/genvk.py
@@ -280,7 +280,7 @@
         protectFeature    = False,
         protectProto      = True,
         protectProtoStr   = 'VK_PROTOTYPES',
-        apicall           = '',
+        apicall           = 'VKAPI_ATTR ',
         apientry          = 'VKAPI_CALL ',
         apientryp         = 'VKAPI_PTR *',
         alignFuncParam    = 48,