Add cross-platform build support for geph5-client on Ubuntu, Windows,… #49

Job	Run time
build (ubuntu-latest, x86_64-unknown-linux-musl)	2m 58s
build (windows-latest, x86_64-pc-windows-msvc)	2m 43s
build (macos-latest, x86_64-apple-darwin)	2m 38s
	8m 19s

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