cmake build invokes ldconfig

[gdt]

The cmake build invokes ldconfig. This is more or less a Linux thing, so it's odd that a build for Mac and Windows invokes it, but that's not important.

Invoking ldconfig is nonportable, and it's also tricky on Linux. Most packages don't call ldconfig, and a normal expectation would be for that to happen outside of package building or package installation.

If ldconfig is going to be run, it needs to be guarded so that all of the following are true:

• ldconfig is only run on Linux, or some set of systems known to want ldconfig
• ldconfig is only run if running as root
• ldconfig is only run if DESTDIR is not set

Overall, I would suggest entirely removing it.