Ninja Multi-Config: Restore TARGET_OBJECTS support in cross-configs

Since commit 2ae72ef7 (Xcode: Enable multi-arch TARGET_OBJECTS genex
in [INTERFACE_]LINK_LIBRARIES, 2021-05-26, v3.21.0-rc1~126^2) the
TARGET_OBJECTS genex, when referenced for linking, is now evaluated with
EvaluateForBuildsystem enabled.  This causes the object file paths to be
computed with a buildsystem-specific placeholder for the configuration.

This is normally fine because the placeholder will be evaluated by the
native buildsystem tool using the proper configuration.  However, the
Ninja Multi-Config generator's `${CONFIGURATION}` placeholder may not
have the correct value for cross-config object files.  Switch back to
using the per-config location of each object file for this generator.

Fixes: #22436