-version-file option; detailed -version information

[andrew-appel]

Invoking clightgen --help describes an option -version-file but invoking clightgen -version-file foo says ccomp: error: Unknown option -version-file (in CompCert 3.8).

I am not advocating for restoring this option, I suggest removing it from the help message.

Also, it would be helpful if either the -version option or some other option could make clightgen and ccomp say more about their configuration, i.e., target architecture. This is useful when a cross-compiler is installed. Of course, one can always obtain this by doing clightgen empty.c and then examining the beginning of empty.v.

[xavierleroy]

Well spotted, thank you. Commit 1a52f58 updates the help message.

Concerning printing the configuration, I'm still undecided, so I'll leave this issue open.

[xavierleroy]

Related to #362.