[index] If the 'external_source_symbol' attribute indicates 'Swift' as the language then report it accordingly

llvm-svn: 301183
diff --git a/clang/include/clang-c/Index.h b/clang/include/clang-c/Index.h
index 1ac2b7f..9acc9b7 100644
--- a/clang/include/clang-c/Index.h
+++ b/clang/include/clang-c/Index.h
@@ -5600,7 +5600,8 @@
   CXIdxEntityLang_None = 0,
   CXIdxEntityLang_C    = 1,
   CXIdxEntityLang_ObjC = 2,
-  CXIdxEntityLang_CXX  = 3
+  CXIdxEntityLang_CXX  = 3,
+  CXIdxEntityLang_Swift  = 4
 } CXIdxEntityLanguage;
 
 /**