Resolve Metal compilation errors for sdcpp

[beebopkim]

Resolves following compilation errors on macOS with LLAMA_METAL=1

In file included from otherarch/sdcpp/sdtype_adapter.cpp:11:
./otherarch/sdcpp/stable-diffusion.cpp:127:9: error: use of undeclared identifier 'ggml_metal_log_set_callback'; did you mean 'ggml_backend_metal_log_set_callback'?
        ggml_metal_log_set_callback(ggml_log_callback_default, nullptr);
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~
        ggml_backend_metal_log_set_callback
./ggml-metal.h:43:15: note: 'ggml_backend_metal_log_set_callback' declared here
GGML_API void ggml_backend_metal_log_set_callback(ggml_log_callback log_callback, void * user_data);
              ^
In file included from otherarch/sdcpp/sdtype_adapter.cpp:13:
./otherarch/sdcpp/upscaler.cpp:24:9: error: use of undeclared identifier 'ggml_metal_log_set_callback'; did you mean 'ggml_backend_metal_log_set_callback'?
        ggml_metal_log_set_callback(ggml_log_callback_default, nullptr);
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~
        ggml_backend_metal_log_set_callback
./ggml-metal.h:43:15: note: 'ggml_backend_metal_log_set_callback' declared here
GGML_API void ggml_backend_metal_log_set_callback(ggml_log_callback log_callback, void * user_data);
              ^
otherarch/sdcpp/sdtype_adapter.cpp:190:28: warning: result of comparison against a string literal is unspecified (use an explicit string comparison function instead) [-Wstring-compare]
    if(inputs.sample_method=="euler a") //all lowercase
                           ^ ~~~~~~~~~
8 warnings and 2 errors generated.
make: *** [sdcpp_default.o] Error 1
make: *** Waiting for unfinished jobs....

[LostRuins]

thanks! i dont have a mac so thanks for helping.