Conditionally write fc_version.h and fc_version

[jwrober]

Closes #879

[lmoureaux]

So it will only update on a new checkout... is it the intended behavior?

[jwrober]

So it will only update on a new checkout... is it the intended behavior?

So it will work from a new created build directory and it will work with code changes post build to only rebuild those files that need updating based on the changes. It won't work if you run a subsequent configure in an existing build directory. I don't see that as much of an issue per se. I think typical workflow is to delete the build directory after a fresh pull or checkout so it works in that scenario too. All that said, I do think it will have the intended effect.

[lmoureaux]

I tend to never delete my build directories, so in a year from now I might still be using the same version...

[jwrober]

I tend to never delete my build directories, so in a year from now I might still be using the same version...

Interesting. I'm surprised you don't run into configuration issues with all the changes we have made. Do you want to handle this with a different approach?

[lmoureaux]

I think merging this would be good to get rid of #879. Eventually we may want to:

1. Move the values to a .cpp file
2. Generate a temporary file, compare it with the existing one and replace only if they're different