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_llvm/llvm-wrapper/RustWrapper.cpp

@@ -1636,6 +1636,10 @@ extern "C" void LLVMRustSetVisibility(LLVMValueRef V,
   LLVMSetVisibility(V, fromRust(RustVisibility));
 }
 
+extern "C" void LLVMRustSetDSOLocal(LLVMValueRef Global, bool is_dso_local) {
+  unwrap<GlobalValue>(Global)->setDSOLocal(is_dso_local);
+}
+
 struct LLVMRustModuleBuffer {
   std::string data;
 };