vulkan backend is broken

[abadams]

abadams@anadams-work:~/projects/Halide_main/apps/local_laplacian
$ HL_TARGET=host-vulkan make test
bin/host/local_laplacian.generator -g local_laplacian -e static_library,h,registration,stmt,assembly -o bin/host-vulkan -f local_laplacian target=host-vulkan
Internal Error at /home/abadams/projects/Halide_main/src/CodeGen_Vulkan_Dev.cpp:2527 triggered by user code at :
map_simt_builtin called on bad variable name: .thread_id_x
make: *** [Makefile:14: bin/host-vulkan/local_laplacian.a] Aborted (core dumped)

This seems related to #8133

[abadams]

This is #8258