cmake: cxxopts is not arch independent when built with ICU support

Since it links to an architecture dependent ICU

cmake/cxxopts.cmake

@@ -87,23 +87,25 @@ endfunction()
 
 # Helper function to ecapsulate install logic
 function(cxxopts_install_logic)
-    if(CMAKE_LIBRARY_ARCHITECTURE)
-        string(REPLACE "/${CMAKE_LIBRARY_ARCHITECTURE}" "" CMAKE_INSTALL_LIBDIR_ARCHIND "${CMAKE_INSTALL_LIBDIR}")
+    if(NOT CXXOPTS_USE_UNICODE_HELP)
+        if(CMAKE_LIBRARY_ARCHITECTURE)
+            string(REPLACE "/${CMAKE_LIBRARY_ARCHITECTURE}" "" CMAKE_INSTALL_LIBDIR_ARCHIND "${CMAKE_INSTALL_LIBDIR}")
+        else()
+            # On some systems (e.g. NixOS), `CMAKE_LIBRARY_ARCHITECTURE` can be empty
+            set(CMAKE_INSTALL_LIBDIR_ARCHIND "${CMAKE_INSTALL_DATAROOTDIR}")
+        endif()
+        if(${CMAKE_VERSION} VERSION_GREATER "3.14")
+            set(OPTIONAL_ARCH_INDEPENDENT "ARCH_INDEPENDENT")
+        endif()
     else()
-        # On some systems (e.g. NixOS), `CMAKE_LIBRARY_ARCHITECTURE` can be empty
-        set(CMAKE_INSTALL_LIBDIR_ARCHIND "${CMAKE_INSTALL_DATAROOTDIR}")
+        set(CMAKE_INSTALL_LIBDIR_ARCHIND "${CMAKE_INSTALL_LIBDIR}")
     endif()
     set(CXXOPTS_CMAKE_DIR "${CMAKE_INSTALL_LIBDIR_ARCHIND}/cmake/cxxopts" CACHE STRING "Installation directory for cmake files, relative to ${CMAKE_INSTALL_PREFIX}.")
     set(version_config "${PROJECT_BINARY_DIR}/cxxopts-config-version.cmake")
     set(project_config "${PROJECT_BINARY_DIR}/cxxopts-config.cmake")
     set(targets_export_name cxxopts-targets)
     set(PackagingTemplatesDir "${PROJECT_SOURCE_DIR}/packaging")
 
-
-    if(${CMAKE_VERSION} VERSION_GREATER "3.14")
-        set(OPTIONAL_ARCH_INDEPENDENT "ARCH_INDEPENDENT")
-    endif()
-
     # Generate the version, config and target files into the build directory.
     write_basic_package_version_file(
         ${version_config}