examples : set the C++ standard to C++17 for server (#3261)

examples : set the C++ standard to C++17 for server (#3261)

This commit updates the server example to use C++17 as the standard.

The motivation for this change is that currently the ci-run
`ggml-100-mac-m4` is failing when compiling the server example on
macOS. The `talk-llama` example also has this setting so it looks like
an alright change to make.

ggml-ci

Refs: https://github.com/ggml-org/ci/tree/results/whisper.cpp/2a/4d6db7d90899aff3d58d70996916968e4e0d27/ggml-100-mac-m4