Told cmake to install ggml-cpp.h as a public header file. (ggml/1126)

It is used by Whisper talk-llama example.

Co-authored-by: Petter Reinholdtsen <pere@debian.org>

ggml/CMakeLists.txt

@@ -250,6 +250,7 @@ set(GGML_PUBLIC_HEADERS
     include/ggml-backend.h
     include/ggml-blas.h
     include/ggml-cann.h
+    include/ggml-cpp.h
     include/ggml-cuda.h
     include/ggml-kompute.h
     include/ggml-opt.h