ninjabackend: Fix a couple of rust bugs

There are two bugs here, first is that we open coded the output args,
instead of using the compiler method. The second is that rust args are
not passed down to the backend invocation.

mesonbuild/backend/ninjabackend.py

@@ -1489,7 +1489,7 @@ int dummy;
         self.create_target_source_introspection(target, valac, args, all_files, [])
         return other_src[0], other_src[1], vala_c_src
 
-    def generate_rust_target(self, target):
+    def generate_rust_target(self, target: build.BuildTarget) -> None:
         rustc = target.compilers['rust']
         # Rust compiler takes only the main file as input and
         # figures out what other files are needed via import
@@ -1539,7 +1539,8 @@ int dummy;
         depfile = os.path.join(target.subdir, target.name + '.d')
         args += ['--emit', 'dep-info={}'.format(depfile), '--emit', 'link']
         args += target.get_extra_args('rust')
-        args += ['-o', os.path.join(target.subdir, target.get_filename())]
+        args += rustc.get_output_args(os.path.join(target.subdir, target.get_filename()))
+        args += self.environment.coredata.get_external_args(target.for_machine, rustc.language)
         orderdeps = [os.path.join(t.subdir, t.get_filename()) for t in target.link_targets]
         linkdirs = OrderedDict()
         for d in target.link_targets: