vlc_fixup: fix usage of typeof from C++

Replace typeof by a decltype()-based equivalent on compilers not
supporting typeof.

Decltype is not equivalent to typeof, but we are mostly concerned about
removing references from the type, since it has no use in C code like
VLC list.

Note that this fixup is there to fix the usage of headers using typeof
in C++ code, not to provide "typeof" directly C++ to replace decltype.

include/vlc_fixups.h

@@ -684,4 +684,11 @@ int clock_nanosleep(clockid_t clock_id, int flags,
 } /* extern "C" */
 #endif
 
+#if defined(__cplusplus)
+#ifndef HAVE_CXX_TYPEOF
+# include <type_traits>
+# define typeof(t) std::remove_reference<decltype(t)>::type
+#endif
+#endif
+
 #endif /* !LIBVLC_FIXUPS_H */