Make clang_Cursor_getMangling not mangle if the declaration isn't mangled

Right now clang_Cursor_getMangling will attempt to mangle any
declaration, even if the declaration isn't mangled (extern C).  This
results in a partially mangled name which isn't useful for much. This
patch makes clang_Cursor_getMangling return an empty string if the
declaration isn't mangled.

Patch by Michael Wu <mwu@mozilla.com>.

llvm-svn: 249639
diff --git a/clang/tools/c-index-test/c-index-test.c b/clang/tools/c-index-test/c-index-test.c
index eeeb832..346bcc6 100644
--- a/clang/tools/c-index-test/c-index-test.c
+++ b/clang/tools/c-index-test/c-index-test.c
@@ -1429,6 +1429,8 @@
 
 static enum CXChildVisitResult PrintMangledName(CXCursor cursor, CXCursor p,
                                                 CXClientData d) {
+  if (clang_isUnexposed(clang_getCursorKind(cursor)))
+    return CXChildVisit_Recurse;
   CXString MangledName;
   PrintCursor(cursor, NULL);
   MangledName = clang_Cursor_getMangling(cursor);