non-cython-mode: Check if should use cpp files instead of c

setup.py

@@ -1157,7 +1157,12 @@ def get_extensions_from_sources(sources):
         c_depends = [expand(src_path, x) for x in flags.pop('c_depends', [])]
         if not can_use_cython:
             # can't use cython, so use the .c files instead.
-            pyx_path = '%s.c' % pyx_path[:-4]
+            _lang = flags.get('language', 'c')
+            if _lang == 'c++':
+                _extension = "cpp"
+            else:
+                _extension = "c"
+                pyx_path = f"{pyx_path[:-4]}.{_extension}"
         if is_graphics:
             depends = resolve_dependencies(pyx_path, depends)
         f_depends = [x for x in depends if x.rsplit('.', 1)[-1] in (