tests : Fix compilation warnings (Linux/GCC) (#2451)

* fix hellaswag print format, cast away warning in test-double-float

* c++11 cannot use designated initializers

* add static to test-grad0.c internal functions

* use memcpy in test-double-float.c

* port c tests to c++

* use initializer list for ggml_init_params

scripts/sync-ggml.sh

@@ -10,5 +10,5 @@ cp -rpv ../ggml/src/ggml-metal.m     ./ggml-metal.m
 cp -rpv ../ggml/src/ggml-metal.metal ./ggml-metal.metal
 cp -rpv ../ggml/include/ggml/ggml.h  ./ggml.h
 
-cp -rpv ../ggml/tests/test-opt.c    ./tests/test-opt.c
-cp -rpv ../ggml/tests/test-grad0.c  ./tests/test-grad0.c
+cp -rpv ../ggml/tests/test-opt.cpp    ./tests/test-opt.cpp
+cp -rpv ../ggml/tests/test-grad0.cpp  ./tests/test-grad0.cpp