...which, somewhat arbitrarily, expects GNU extension __attribute__((...)) to
come before MSVC extension __declspec(...) with

  MaybeParseGNUAttributes(attrs);
  MaybeParseMicrosoftDeclSpecs(attrs);

in Parser::ParseClassSpecifier (lib/Parse/ParseDeclCXX.cpp).

Change-Id: I5936558c8fc08b278575b6c678cde6eccd4647fb