cmake: clearly indicate how to build without CUDA/Kompute on failure

Signed-off-by: Jared Van Bortel <jared@nomic.ai>

gpt4all-backend/CMakeLists.txt

@@ -65,6 +65,11 @@ if (LLMODEL_VULKAN)
     list(APPEND BUILD_VARIANTS vulkan vulkan-avxonly)
 endif()
 if (LLMODEL_CUDA)
+    include(CheckLanguage)
+    check_language(CUDA)
+    if (NOT CMAKE_CUDA_COMPILER)
+        message(WARNING "CUDA Toolkit not found. To build without CUDA, use -DLLMODEL_CUDA=OFF.")
+    endif()
     enable_language(CUDA)
     list(APPEND BUILD_VARIANTS cuda cuda-avxonly)
 endif()

gpt4all-backend/llama.cpp.cmake

@@ -542,10 +542,13 @@ function(include_ggml SUFFIX)
         endif()
         message(STATUS "Kompute found")
 
-        find_package(Vulkan COMPONENTS glslc REQUIRED)
+        find_package(Vulkan COMPONENTS glslc)
+        if (NOT Vulkan_FOUND)
+            message(FATAL_ERROR "Vulkan not found. To build without Vulkan, use -DLLMODEL_KOMPUTE=OFF.")
+        endif()
         find_program(glslc_executable NAMES glslc HINTS Vulkan::glslc)
         if (NOT glslc_executable)
-            message(FATAL_ERROR "glslc not found")
+            message(FATAL_ERROR "glslc not found. To build without Vulkan, use -DLLMODEL_KOMPUTE=OFF.")
         endif()
 
         function(compile_shader)