graphics/vulkan-loader: unbreak with devel/vulkan-validation-layers

In file included from /usr/ports/graphics/vulkan-loader/work/Vulkan-Loader-sdk-1.2.135.0/loader/debug_utils.c:39:
In file included from /usr/local/include/vk_object_types.h:35:
/usr/local/include/cast_utils.h:24:10: fatal error: 'cassert' file not found
#include <cassert>

^~~~~~~~~

PR: 247075
Reported by: nick.rozhkov@gmail.com