Xcode: Fix object library builds with sanitizers enabled

Using `xcodebuild -enableAddressSanitizer YES ...` causes object files
to be placed in a different directory name.  Xcode provides a
placeholder for this that we can use in `OTHER_LDFLAGS` to reference
object files for linking the dependents of object libraries.  However,
CMake's features for installing and exporting object libraries depend on
knowing the real path with no placeholders.  For these cases, use the
default object directory.  Users will then have to choose between
sanitizers and the installation and export features, but both will work
individually.

Fixes: #16289
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