Simplify FindExternalVisibleDeclsByName by making it return a bool indicating

if it found any decls, rather than returning a list of found decls. This
removes a returning-ArrayRef-to-deleted-storage bug from
MultiplexExternalSemaSource (in code not exercised by any of the clang
binaries), reduces the work required in the found-no-decls case with PCH, and
importantly removes the need for DeclContext::lookup to be reentrant.

No functionality change intended!

llvm-svn: 174576

clang/lib/Frontend/ChainedIncludesSource.cpp

@@ -191,7 +191,7 @@ CXXBaseSpecifier *
 ChainedIncludesSource::GetExternalCXXBaseSpecifiers(uint64_t Offset) {
   return getFinalReader().GetExternalCXXBaseSpecifiers(Offset);
 }
-DeclContextLookupResult
+bool
 ChainedIncludesSource::FindExternalVisibleDeclsByName(const DeclContext *DC,
                                                       DeclarationName Name) {
   return getFinalReader().FindExternalVisibleDeclsByName(DC, Name);