[LTO] Fix cloning of llvm*.used when splitting module

Refines the fix in 3c4c2050 to only
put globals whose defs were cloned into the split regular LTO module
on the cloned llvm*.used globals. This avoids an issue where one of the
attached values was a local that was promoted in the original module
after the module was cloned. We only need to have the values defined in
the new module on those globals.

Fixes PR49251.

Differential Revision: https://reviews.llvm.org/D97013