Pull Request being offered, thank you, I find is pushing us to pick a standard.

The GNU vs. XDG debacle (first I've heard of it) is not even a choice you have to make. The "GNU" in GNUInstallDirs I believe was chosen arbitrarily, not out of some dismissal of XDG standard; there is no XDGInstallDirs CMake module, the one named with GNU is the only one like it.

The reason for merging this change would be simply to allow overriding the bindir name. E.g. -DCMAKE_INSTALL_BINDIR=libexec or =/opt/foo/binaries. With the current code, you can't do that. If you use "make install" to install it, the paths are hardcoded to prefix + bin, lib, share, etc.

The default paths provided by GNUInstallDirs are the same as what is hardcoded in the current code.

All I wanted to do with this PR is, in a standard way, allow packagers to override the install paths instead of having to manually move files around after the install.