fix multilib error on emerge (#39)

Fix multilib error.

Author: will-riley

CMakeLists.txt

@@ -9,6 +9,7 @@ if(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
     set(CMAKE_INSTALL_PREFIX "${CMAKE_BINARY_DIR}/install" CACHE PATH "..." FORCE)
 endif()
 
+set(CMAKE_INSTALL_LIBDIR "/lib64")
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)