Make max_input_size a function (GCC -Wunused-const-variable)

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/detail/view/node.hpp

@@ -32,7 +32,10 @@ static_assert(static_cast<std::uint8_t>(value_t::null) == 0 && static_cast<std::
 /// The largest input a document accepts, in bytes. Offsets and node counts are
 /// 32 bits wide; the limit keeps 16 bytes (the width of the scanner's steps)
 /// below 2^32, so that a position one step past the end of the text fits.
-static constexpr std::size_t max_input_size = 0xFFFFFFEFu;
+constexpr std::size_t max_input_size() noexcept
+{
+    return 0xFFFFFFEFu;
+}
 
 /// node flags
 struct node_flags