Fix compilation on Pop!_OS 22.04 LTS CUDA

Downgrade the C++ version from 17 to 14, and also update the code to remove compilation warnings.

ggml/CMakeLists.txt

@@ -195,7 +195,11 @@ option(GGML_BUILD_EXAMPLES "ggml: build examples" ${GGML_STANDALONE})
 set(CMAKE_C_STANDARD 11)
 set(CMAKE_C_STANDARD_REQUIRED true)
 
+if (GGML_SYCL)
     set(CMAKE_CXX_STANDARD 17)
+else()
+    set(CMAKE_CXX_STANDARD 14)
+endif()
 set(CMAKE_CXX_STANDARD_REQUIRED true)
 
 set(THREADS_PREFER_PTHREAD_FLAG ON)

ggml/src/ggml-cuda/ggml-cuda.cu

@@ -2693,6 +2693,8 @@ bool ggml_backend_cuda_register_host_buffer(void * buffer, size_t size) {
     }
     return true;
 #else
+    (void)buffer;
+    (void)size;
     return false;
 #endif
 }