[ELF] Prevent internalizing used comdat symbol

When a comdat symbol is defined in both bitcode and regular object
files, which are contained in the same archive, the linker could lose
the flag that the symbol is used in the regular object file and allow
LTO to internalize it, which led to "error: undefined symbol".

The issue was introduced in D79300.

Differential Revision: https://reviews.llvm.org/D114801