sync : ggml (ggml-backend) (#3548)

* sync : ggml (ggml-backend)

ggml-ci

* zig : add ggml-backend to the build

CMakeLists.txt

@@ -663,6 +663,8 @@ add_library(ggml OBJECT
             ggml.h
             ggml-alloc.c
             ggml-alloc.h
+            ggml-backend.c
+            ggml-backend.h
             ${GGML_SOURCES_CUDA} ${GGML_HEADERS_CUDA}
             ${GGML_SOURCES_OPENCL} ${GGML_HEADERS_OPENCL}
             ${GGML_SOURCES_METAL} ${GGML_HEADERS_METAL}