cmake : add ggml public headers (#5011)

CMakeLists.txt

@@ -846,7 +846,7 @@ install(FILES ${CMAKE_CURRENT_BINARY_DIR}/LlamaConfig.cmake
               ${CMAKE_CURRENT_BINARY_DIR}/LlamaConfigVersion.cmake
         DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/Llama)
 
-set(GGML_PUBLIC_HEADERS "ggml.h"
+set(GGML_PUBLIC_HEADERS "ggml.h" "ggml-alloc.h" "ggml-backend.h"
         "${GGML_HEADERS_CUDA}" "${GGML_HEADERS_OPENCL}"
         "${GGML_HEADERS_METAL}" "${GGML_HEADERS_MPI}" "${GGML_HEADERS_EXTRA}")