properly set lib dir for 64 bit systems

[sergey-safarov]

No description provided.

[andywolk]

This is from our CI:

-- Found PkgConfig: /usr/bin/pkg-config (found version "0.29") -- Checking for module 'uuid' -- Found uuid, version 2.33.1 Found UUID setup target at imported location: /usr/lib/x86_64-linux-gnu/libuuid.so -- Found OpenSSL: /usr/lib/x86_64-linux-gnu/libcrypto.so (found version "1.1.1n") -- Found OpenSSL: /usr/lib/x86_64-linux-gnu/libcrypto.so (found version "1.1.1n") found components: Crypto SSL -- Looking for pthread.h -- Looking for pthread.h - found -- Looking for pthread_create -- Looking for pthread_create - not found -- Check if compiler accepts -pthread -- Check if compiler accepts -pthread - yes -- Found Threads: TRUE -- Performing Test COMPILER_HAS_HIDDEN_VISIBILITY -- Performing Test COMPILER_HAS_HIDDEN_VISIBILITY - Success Compiler supports visibility CMake Error at CMakeLists.txt:559 (install): install TARGETS given no LIBRARY DESTINATION for shared library target "ks2". -- Configuring incomplete, errors occurred! 

[sergey-safarov]

Could you execute this test commands

wget https://raw.githubusercontent.com/sergey-safarov/libks/tmp/pkg/rpm/libks.spec rpmbuild -bb --undefine _disable_source_fetch libks.spec 

Expected result, compiled rpm packages.
Tested on CentOS 8 stream.