Auto merge of #116183 - cjgillot:debug-dse-always, r=oli-obk

Always preserve DebugInfo in DeadStoreElimination.

This is a version of #106852 that does not check the current crate's debuginfo flag, and always attempts to preserve debuginfo.

I haven't figured out how to handle mixing debuginfo levels for std, the one for the test, and the one for the CI target just right to merge #106852, so this can at least fix the debuginfo issue.

Fixes rust-lang/rust#103655

Author: bors