properly set lib dir for 64 bit systems

[sergey-safarov]

[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.