[cmake] don't hardcode lib, include install path
[cmake] don't hardcode lib, include install path

On fedora (and probably others) the installation path for libs
is /usr/lib64 on 64 bit systems. This patch uses
 LIB_INSTALL_DIR        default "lib"
 INCLUDE_INSTALL_DIR    default "include"
instead of hardcoded values that can be used by the build system
to configure the paths.

stoewer/nix