ollama: fix vulkan variant — wire SPIRV-Headers across the ExternalProject boundary

Two layers were missing for ollama-vulkan after the 0.30.x bump's switch to
per-accelerator runners via ExternalProject_Add:

1. spirv-headers wasn't in nativeBuildInputs, so the parent cmake configure
   never even saw `SPIRV-HeadersConfig.cmake`. Add it (header-only — native
   is the right slot).

2. The runner sub-builds (`ollama-llama-server-vulkan` et al.) are launched
   by `cmake/local.cmake`'s `ExternalProject_Add`, whose child cmake process
   inherits env vars but not the parent's `-D` flags. Even after fixing
   (1), the child's `find_package(SPIRV-Headers REQUIRED)` at
   `ggml-vulkan/CMakeLists.txt:14` couldn't see the config, and once that
   was worked around with `CMAKE_PREFIX_PATH` as env, the compile then
   failed with `fatal error: spirv/unified1/spirv.hpp` — because
   upstream's `target_link_libraries(ggml-vulkan PRIVATE Vulkan::Vulkan)`
   notably does NOT link `SPIRV-Headers::SPIRV-Headers`, so the interface
   include path the cmake config exports never flows into the compile
   commands. Force the include via `NIX_CFLAGS_COMPILE` rather than
   patching upstream's CMakeLists across llama.cpp pins.

Verified: `ollama-vulkan` builds end-to-end; `$out/lib/ollama/vulkan/libggml-vulkan.so`
is present (not a silent CPU fallback like the cuda variant suffered in
the first 0.30 attempt).

🤖 Assisted by Claude

pkgs/by-name/ol/ollama/package.nix

@@ -21,6 +21,7 @@
   vulkan-tools,
   vulkan-headers,
   vulkan-loader,
+  spirv-headers,
   shaderc,
   ccache,
 
@@ -191,6 +192,10 @@ goBuild (finalAttrs: {
   ]
   ++ lib.optionals enableVulkan [
     ccache
+    # ggml-vulkan/CMakeLists.txt does `find_package(SPIRV-Headers REQUIRED)`
+    # at configure time (it builds shader code into the vulkan backend).
+    # Header-only — nativeBuildInputs is the right slot.
+    spirv-headers
   ];
 
   buildInputs =
@@ -276,6 +281,28 @@ goBuild (finalAttrs: {
 
     in
     ''
+      ${lib.optionalString enableVulkan ''
+        # Ollama builds each per-accelerator llama.cpp runner via
+        # cmake/local.cmake's ExternalProject_Add(ollama-llama-server-vulkan …).
+        # Two things need to cross the parent → child boundary:
+        #
+        # 1. The SPIRV-Headers cmake config — so `find_package(SPIRV-Headers
+        #    REQUIRED)` at ggml-vulkan/CMakeLists.txt:14 succeeds in the
+        #    child. CMAKE_PREFIX_PATH as a flag wouldn't propagate; as env
+        #    var it does.
+        # 2. The SPIRV-Headers include directory in the compile env. The
+        #    ggml-vulkan target's `target_link_libraries(... Vulkan::Vulkan)`
+        #    notably does NOT link `SPIRV-Headers::SPIRV-Headers`, so the
+        #    interface include directory the cmake config exports never
+        #    flows into the compile commands — even though the find_package
+        #    call succeeded. `#include <spirv/unified1/spirv.hpp>` then
+        #    fails at compile time. Patching upstream's CMakeLists for
+        #    one missing link line is fragile across llama.cpp pins;
+        #    NIX_CFLAGS_COMPILE forces the include path globally and
+        #    survives version bumps.
+        export CMAKE_PREFIX_PATH="${spirv-headers}''${CMAKE_PREFIX_PATH:+:$CMAKE_PREFIX_PATH}"
+        export NIX_CFLAGS_COMPILE="-isystem ${spirv-headers}/include $NIX_CFLAGS_COMPILE"
+      ''}
       cmake -B build \
         -DCMAKE_SKIP_BUILD_RPATH=ON \
         -DCMAKE_BUILD_WITH_INSTALL_RPATH=ON \