According to https://cmake.org/cmake/help/v3.0/module/GNUInstallDirs.html
`${CMAKE_INSTALL_LIBDIR} ` is only variable which should be used as base
directory. Without that patch on 64 bit archs libraries, cmake modules and
pkgconfig file are installed for example in /usr/lib6464 base directory.
This patch fixes#4621.
Signed-off-by: Tomasz Kłoczko <koczek@github.com>
