Default to the medium code model on OpenHarmony LoongArch target

The context for this is #130266: setting the medium code model for the
'loongarch64-linux-ohos' target.

Author: heiher

compiler/rustc_target/src/spec/targets/loongarch64_unknown_linux_ohos.rs

@@ -1,4 +1,4 @@
-usecrate::spec::{SanitizerSet,Target,TargetOptions, base};
+usecrate::spec::{CodeModel,SanitizerSet,Target,TargetOptions, base};
 
 pub(crate)fntarget() -> Target{
 Target{
@@ -13,6 +13,7 @@ pub(crate) fn target() -> Target {
 data_layout:"e-m:e-p:64:64-i64:64-i128:128-n32:64-S128".into(),
 arch:"loongarch64".into(),
 options:TargetOptions{
+code_model:Some(CodeModel::Medium),
 cpu:"generic".into(),
 features:"+f,+d".into(),
 llvm_abiname:"lp64d".into(),