Demangler: Fix constructor cv qualifier handling

Previously if we parsed a constructor then we set parsed_ctor_dtor_cv
to true and never reseted it. This causes issue when a template argument
references a constructor (e.g. type of lambda defined inside a
constructor) as we will have the parsed_ctor_dtor_cv flag set what will
cause issues when parsing later arguments.

Differential Revision: https://reviews.llvm.org/D33385
libcxxabi change: https://reviews.llvm.org/rL303737

llvm-svn: 303738

llvm/lib/Demangle/ItaniumDemangle.cpp

@@ -4030,6 +4030,8 @@ static const char *parse_encoding(const char *first, const char *last, C &db) {
     save_value<decltype(db.tag_templates)> sb(db.tag_templates);
     if (db.encoding_depth > 1)
       db.tag_templates = true;
+    save_value<decltype(db.parsed_ctor_dtor_cv)> sp(db.parsed_ctor_dtor_cv);
+    db.parsed_ctor_dtor_cv = false;
     switch (*first) {
     case 'G':
     case 'T':