Use single vk_api_xml for scripts

meson.build

@@ -179,6 +179,7 @@ endif
 
 dep_pthread = cc.find_library('pthread')
 
+vk_api_xml = files('modules/Vulkan-Docs/xml/vk.xml')
 vk_layer_table_helpers = []
 loader_genvk_py = files('modules/Vulkan-Loader/scripts/loader_genvk.py')
 foreach s : ['vk_dispatch_table_helper.h', 'vk_layer_dispatch_table.h']#, 'vk_loader_extensions.h', 'vk_loader_extensions.c']
@@ -186,11 +187,10 @@ foreach s : ['vk_dispatch_table_helper.h', 'vk_layer_dispatch_table.h']#, 'vk_lo
     s, output : s,
     command : [prog_python, loader_genvk_py,
       '-scripts', '../../Vulkan-Docs/scripts', # relative to loader_genvk.py
-      '-registry', join_paths(meson.source_root(), 'modules/Vulkan-Docs/xml/vk.xml'),
+      '-registry', vk_api_xml,
       '-o','@OUTDIR@', s])
 endforeach
 
-vk_api_xml = files('modules/Vulkan-Docs/xml/vk.xml')
 vk_enum_to_str = custom_target(
   'vk_enum_to_str',
   input : ['bin/gen_enum_to_str.py', vk_api_xml],