Fix install target in non-Wayland systems

[Jose123456]

On systems that don't have the Wayland client libraries installed, the install target fails with

mkdir -p ./usr/local/lib
install -m 644  \
    ./usr/local/lib/
usage: install [-bCcpSsUv] [-f flags] [-g group] [-m mode] [-o owner]
               [-M log] [-D dest] [-h hash] [-T tags]
               [-B suffix] [-l linkflags] [-N dbdir]
               file1 file2
       install [-bCcpSsUv] [-f flags] [-g group] [-m mode] [-o owner]
               [-M log] [-D dest] [-h hash] [-T tags]
               [-B suffix] [-l linkflags] [-N dbdir]
               file1 ... fileN directory
       install -dU [-vU] [-g group] [-m mode] [-N dbdir] [-o owner]
               [-M log] [-D dest] [-h hash] [-T tags]
               directory ...
gmake[1]: *** [Makefile:312: WAYLAND_LIB_install] Error 64
gmake[1]: Leaving directory '/usr/home/jose/gitrepos/nvidia-settings/src'
gmake: *** [Makefile:23: install] Error 2

[Jose123456]

In the unlikely event it makes a difference, this has now been accepted by the FreeBSD Ports Collection:
https://cgit.freebsd.org/ports/commit/?id=e78bd9997228767faf80d75121a5feedc2d544d0

[Jose123456]

Closes: #119