Only block when building with MSVC (#15719)

Author: JacobSzwejbka

tools/cmake/preset/llm.cmake

@@ -16,13 +16,21 @@ set_overridable_option(EXECUTORCH_BUILD_EXTENSION_TENSOR ON)
 set_overridable_option(EXECUTORCH_BUILD_KERNELS_OPTIMIZED ON)
 set_overridable_option(EXECUTORCH_BUILD_XNNPACK ON)
 
-# Turn on the quantized and LLM kernels unless on windows cuda build which
-# currently doesn't support this due to using msvc.
-if(NOT (EXECUTORCH_BUILD_CUDA AND (CMAKE_SYSTEM_NAME STREQUAL "Windows"
-                                   OR CMAKE_SYSTEM_NAME STREQUAL "WIN32"))
+# Turn on the quantized and LLM kernels unless on Windows with MSVC build since
+# they don't currently compile.
+if(NOT ((CMAKE_SYSTEM_NAME STREQUAL "Windows" OR CMAKE_SYSTEM_NAME STREQUAL
+                                                 "WIN32") AND MSVC)
 )
   set_overridable_option(EXECUTORCH_BUILD_KERNELS_QUANTIZED ON)
   set_overridable_option(EXECUTORCH_BUILD_KERNELS_LLM ON)
+else()
+  if(NOT EXECUTORCH_BUILD_CUDA)
+    message(
+      WARNING
+        "The llm custom kernels and the quantized kernels will not be built when using MSVC on Windows. "
+        "If you need them (since you appear to be building for CPU) try building with -T ClangCL"
+    )
+  endif()
 endif()
 
 if(CMAKE_SYSTEM_NAME STREQUAL "Darwin")