One might have applications using either at the same time, distributions always ship both

@bluca Are you shure? Why someone need use static and shared libs at the same time?
And about distributions you completely wrong
https://fedoraproject.org/wiki/Packaging:Guidelines#Packaging_Static_Libraries

Packages including libraries SHOULD exclude static libs as far as possible (eg by configuring with --disable-static). Applications linking against libraries SHOULD link against shared libraries not static versions.

I know that's the aspiration, in reality it's a bit different and users often ask for both - anyhow I don't care that much about the default, as long as there's an option for it

Where option for it?

Having a static library installed doesn't make any sense. Static library should only be used during static builds and distributed. We should stick with dynamic library for all systems except windows (mingw)/osx builds.

Or may be you can add parameter to not build static lib at all?

Maybe about the static library build we should do something like the nanomsg project https://github.com/nanomsg/nanomsg/blob/master/CMakeLists.txt#L99

It would be great.

Thanks