ggml-cpu : prevent kleidiai build/install targets

* currently cmake install targets of kleidiai generate error
* set `SOURCE_SUBDIR` to explict invalid path as a bypass
* Add option `EXCLUDE_FROM_ALL` will do the same fix but it requires
  camke > v3.28.

REF: https://discourse.cmake.org/t/prevent-fetchcontent-makeavailable-to-execute-cmakelists-txt/12704/3

Signed-off-by: Yongjoo Ahn <yongjoo1.ahn@samsung.com>

Author: anyj0527

ggml/src/ggml-cpu/CMakeLists.txt

@@ -558,7 +558,9 @@ function(ggml_add_cpu_backend_variant_impl tag_name)
         FetchContent_Declare(KleidiAI_Download
             URL ${KLEIDIAI_DOWNLOAD_URL}
             DOWNLOAD_EXTRACT_TIMESTAMP NEW
-            URL_HASH MD5=${KLEIDIAI_ARCHIVE_MD5})
+            URL_HASH MD5=${KLEIDIAI_ARCHIVE_MD5}
+            SOURCE_SUBDIR pathThatDoesNotExist # Prevent all targets to be executed
+        )
 
         FetchContent_MakeAvailable(KleidiAI_Download)
         FetchContent_GetProperties(KleidiAI_Download
@@ -571,11 +573,6 @@ function(ggml_add_cpu_backend_variant_impl tag_name)
 
         add_compile_definitions(GGML_USE_CPU_KLEIDIAI)
 
-        # Remove kleidiai target after fetching it
-        if (TARGET kleidiai)
-            set_target_properties(kleidiai PROPERTIES EXCLUDE_FROM_ALL TRUE)
-        endif()
-
         list(APPEND GGML_CPU_SOURCES
             ggml-cpu/kleidiai/kleidiai.cpp
             ggml-cpu/kleidiai/kernels.cpp