interpreter: use typed_kwargs for build_target.link_language

mesonbuild/interpreter/kwargs.py

@@ -332,6 +332,7 @@ class _BaseBuildTarget(TypedDict):
     install_mode: FileMode
     install_rpath: str
     implicit_include_directories: bool
+    link_language: T.Optional[str]
     native: MachineChoice
     override_options: T.Dict[OptionKey, T.Union[str, int, bool, T.List[str]]]
     depend_files: NotRequired[T.List[File]]

mesonbuild/interpreter/type_checking.py

@@ -578,6 +578,12 @@ _BUILD_TARGET_KWS: T.List[KwargInfo] = [
     ),
     KwargInfo('build_rpath', str, default='', since='0.42.0'),
     KwargInfo('install_rpath', str, default=''),
+    KwargInfo(
+        'link_language',
+        (str, NoneType),
+        validator=in_set_validator(set(compilers.all_languages)),
+        since='0.51.0',
+    ),
 ]
 
 def _validate_win_subsystem(value: T.Optional[str]) -> T.Optional[str]: