[clangd] Do not insert parentheses when completing a using declaration

Summary:
Would be nice to also fix this in clang, but that looks like more work
if we want to preserve signatures in informative chunks.

Fixes https://github.com/clangd/clangd/issues/118

Reviewers: kadircet

Reviewed By: kadircet

Subscribers: merge_guards_bot, MaskRay, jkorous, arphaman, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D69382
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index 6d4a1a4..c6ffbfc 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -600,7 +600,10 @@
   if (ParseOptionalCXXScopeSpecifier(D.SS, nullptr, /*EnteringContext=*/false,
                                      /*MayBePseudoDtor=*/nullptr,
                                      /*IsTypename=*/false,
-                                     /*LastII=*/&LastII))
+                                     /*LastII=*/&LastII,
+                                     /*OnlyNamespace=*/false,
+                                     /*InUsingDeclaration=*/true))
+
     return true;
   if (D.SS.isInvalid())
     return true;