Add gmock into our dependencies.

third_party/boost/boost/type_traits/is_void.hpp

Index: third_party/boost/boost/type_traits/is_void.hpp
diff --git a/third_party/boost/boost/type_traits/is_void.hpp b/third_party/boost/boost/type_traits/is_void.hpp
new file mode 100644
index 0000000000000000000000000000000000000000..ca51b54870e478ad87de96ce74fcc693e91d0947
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+++ b/third_party/boost/boost/type_traits/is_void.hpp
@@ -0,0 +1,33 @@
+
+//  (C) Copyright Steve Cleary, Beman Dawes, Howard Hinnant & John Maddock 2000.
+//  Use, modification and distribution are subject to the Boost Software License,
+//  Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt).
+//
+//  See http://www.boost.org/libs/type_traits for most recent version including documentation.
+
+#ifndef BOOST_TT_IS_VOID_HPP_INCLUDED
+#define BOOST_TT_IS_VOID_HPP_INCLUDED
+
+#include <boost/config.hpp>
+
+// should be the last #include
+#include <boost/type_traits/detail/bool_trait_def.hpp>
+
+namespace boost {
+
+//* is a type T void - is_void<T>
+BOOST_TT_AUX_BOOL_TRAIT_DEF1(is_void,T,false)
+BOOST_TT_AUX_BOOL_TRAIT_SPEC1(is_void,void,true)
+
+#ifndef BOOST_NO_CV_VOID_SPECIALIZATIONS
+BOOST_TT_AUX_BOOL_TRAIT_SPEC1(is_void,void const,true)
+BOOST_TT_AUX_BOOL_TRAIT_SPEC1(is_void,void volatile,true)
+BOOST_TT_AUX_BOOL_TRAIT_SPEC1(is_void,void const volatile,true)
+#endif
+
+} // namespace boost
+
+#include <boost/type_traits/detail/bool_trait_undef.hpp>
+
+#endif // BOOST_TT_IS_VOID_HPP_INCLUDED