Fix Ninja Multi-Config Cross-Config support

The default output directory was the same for all `$<CONFIG>`s,
which caused conflicting build rules.
The issue probably still exists for the rare case when:
1. The user specified an `OUTPUT_DIRECTORY` property AND
2. did not specify an `OUTPUT_DIRECTORY_$<CONFIG>` property AND
3. The value of the `OUTPUT_DIRECTORY` does not contain a genex,
  depending on the `$<CONFIG>`.

Corrosion could detect and append a `$<CONFIG>` in this case, but
I think leaving this up to the user is reasonable for now.

cmake/Corrosion.cmake

@@ -123,7 +123,7 @@ function(_corrosion_set_imported_location_deferred target_name base_property out
         elseif(output_directory)
             set(curr_out_dir "${output_directory}")
         else()
-            set(curr_out_dir "${CMAKE_CURRENT_BINARY_DIR}")
+            set(curr_out_dir "${CMAKE_CURRENT_BINARY_DIR}/$<CONFIG>")
         endif()
         string(REPLACE "\$<CONFIG>" "${config_type}" curr_out_dir "${curr_out_dir}")
         message(DEBUG "Setting ${base_property}_${config_type_upper} for target ${target_name}"
@@ -233,7 +233,7 @@ function(_corrosion_copy_byproduct_deferred target_name output_dir_prop_names ca
             # Fallback to the default directory. We do not append the configuration directory here
             # and instead let CMake do this, since otherwise the resolving of dynamic library
             # imported paths may fail.
-            set(curr_out_dir "${CMAKE_CURRENT_BINARY_DIR}")
+            set(curr_out_dir "${CMAKE_CURRENT_BINARY_DIR}/$<CONFIG>")
         endif()
         set(multiconfig_out_dir_genex "${multiconfig_out_dir_genex}$<$<CONFIG:${config_type}>:${curr_out_dir}>")
     endforeach()