[CodeGen] Function multi-versioning: don't set comdat for internal linkage resolvers

For function multi-versioning using the target or target_clones
function attributes, currently we incorrectly set comdat for internal
linkage resolvers. This is problematic for ELF linkers
as GRP_COMDAT deduplication will kick in even with STB_LOCAL signature
(https://groups.google.com/g/generic-abi/c/2X6mR-s2zoc
"GRP_COMDAT group with STB_LOCAL signature").

In short, two `__attribute((target_clones(...))) static void foo()`
in two translation units will be deduplicated. Fix this.

Fix #65114

Reviewed By: erichkeane

Differential Revision: https://reviews.llvm.org/D158963