fix(ci): set LIBCLANG_PATH on Linux; install Vulkan via brew on macOS

Two follow-ups to the previous CI deps commit:

1. Linux: libclang-dev installs libclang.so under
   /usr/lib/llvm-*/lib and /usr/lib/x86_64-linux-gnu, but
   bindgen-0.72.1 does not probe the llvm-versioned directory by
   default. Resolve the newest /usr/lib/llvm-*/lib candidate
   dynamically and export LIBCLANG_PATH so bindgen finds it without
   any clang-sys guesswork. Also install glslang-tools + spirv-tools
   so find_package(Vulkan COMPONENTS glslc) succeeds against
   ggml-vulkan's cmake step.

2. macOS: llama-cpp-sys-2 sets GGML_VULKAN=ON unconditionally when
   the vulkan feature is enabled; cmake's find_package(Vulkan) then
   fails on a vanilla macOS-latest runner because there is no
   Vulkan SDK shipped by default. The LunarG macOS SDK ships as a
   non-scriptable interactive installer, so we compose MoltenVK +
   Vulkan loader + headers + shaderc via Homebrew formulae instead.
   Export VULKAN_SDK=$(brew --prefix) and CMAKE_PREFIX_PATH=same so
   both the build.rs branch and cmake's FindVulkan resolve headers /
   libs / glslc from /opt/homebrew.

Applied symmetrically to check.yml and build.yml. Windows config is
unchanged.

Co-authored-by: jars <jakejars@users.noreply.github.com>

.github/workflows/build.yml

@@ -81,14 +81,25 @@ jobs:
             build-essential \
             libclang-dev \
             clang \
-            libvulkan-dev
+            libvulkan-dev \
+            glslang-tools \
+            spirv-tools
+          LIBCLANG_CANDIDATE=$(ls -d /usr/lib/llvm-*/lib 2>/dev/null | sort -V | tail -n1)
+          if [ -z "$LIBCLANG_CANDIDATE" ]; then
+            LIBCLANG_CANDIDATE=/usr/lib/x86_64-linux-gnu
+          fi
+          echo "LIBCLANG_PATH=$LIBCLANG_CANDIDATE" >> "$GITHUB_ENV"
 
       - name: Install macOS deps
         if: matrix.os == 'macos-latest'
         run: |
           brew list cmake >/dev/null 2>&1 || brew install cmake
           brew list llvm >/dev/null 2>&1 || brew install llvm
+          brew install vulkan-headers vulkan-loader molten-vk shaderc
           echo "LIBCLANG_PATH=$(brew --prefix llvm)/lib" >> "$GITHUB_ENV"
+          BREW_PREFIX=$(brew --prefix)
+          echo "VULKAN_SDK=$BREW_PREFIX" >> "$GITHUB_ENV"
+          echo "CMAKE_PREFIX_PATH=$BREW_PREFIX" >> "$GITHUB_ENV"
 
       - name: Install Windows deps
         if: matrix.os == 'windows-latest'