Manually set dso_local when its valid to do so

This should have no real effect in most cases, as e.g. `hidden`
visibility already implies `dso_local` (or at least LLVM IR does not
preserve the `dso_local` setting if the item is already `hidden`), but
it should fix `-Crelocation-model=static` and improve codegen in
executables.

Note that this PR does not exhaustively port the logic in [clang]. Only
the obviously correct portion and what is necessary to fix a regression
from LLVM 12 that relates to `-Crelocation_model=static`.

Fixes #83335

[clang]: 3001d080c8/clang/lib/CodeGen/CodeGenModule.cpp (L945-L1039)

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -254,6 +254,7 @@ pub fn from_fn_attrs(cx: &CodegenCx<'ll, 'tcx>, llfn: &'ll Value, instance: ty::
         attributes::emit_uwtable(llfn, true);
     }
 
+    // FIXME: none of these three functions interact with source level attributes.
     set_frame_pointer_elimination(cx, llfn);
     set_instrument_function(cx, llfn);
     set_probestack(cx, llfn);