Disable NaN render as numpy.nan for older compilers

std::isnan is not available on gcc-4.8

Author: sizmailov

include/pybind11/cast.h

@@ -1871,6 +1871,7 @@ struct arg_v : arg {
     arg_v(const arg &base, T &&x, const char *descr = nullptr)
         : arg_v(arg(base), std::forward<T>(x), descr) { }
 
+#if __cplusplus >= 201103L
 #define ARGV_NAN_DEFAULT_OVERLOAD(FLOAT_TYPE) \
     arg_v(const arg &base, FLOAT_TYPE x) \
         : arg_v(arg(base), x, std::isnan(x) ? "numpy.nan" : nullptr) {}
@@ -1880,6 +1881,7 @@ struct arg_v : arg {
     ARGV_NAN_DEFAULT_OVERLOAD(long double)
 
 #undef ARGV_NAN_DEFAULT_OVERLOAD
+#endif
 
     /// Same as `arg::noconvert()`, but returns *this as arg_v&, not arg&
     arg_v &noconvert(bool flag = true) { arg::noconvert(flag); return *this; }

tests/test_kwargs_and_defaults.cpp

@@ -35,11 +35,12 @@ TEST_SUBMODULE(kwargs_and_defaults, m) {
     m.def("kw_func_udl_z", kw_func, "x"_a, "y"_a=0);
 
     m.def("kw_func_float_123", kw_func_float, "x"_a=1, "y"_a=2, "z"_a=3);
+#if __cplusplus >= 201103L
     m.def("kw_func_float_nan", kw_func_float,
         "x"_a=std::numeric_limits<float>::quiet_NaN(),
         "y"_a=std::numeric_limits<double>::quiet_NaN(),
         "z"_a=std::numeric_limits<long double>::quiet_NaN());
-
+#endif
 
     // test_args_and_kwargs
     m.def("args_function", [](py::args args) -> py::tuple {

tests/test_kwargs_and_defaults.py

@@ -11,7 +11,9 @@ def test_function_signatures(doc):
     assert doc(m.kw_func_udl) == "kw_func_udl(x: int, y: int = 300) -> str"
     assert doc(m.kw_func_udl_z) == "kw_func_udl_z(x: int, y: int = 0) -> str"
     assert doc(m.kw_func_float_123) == "kw_func_float_123(x: float = 1, y: float = 2, z: float = 3) -> str"
-    assert doc(m.kw_func_float_nan) == "kw_func_float_nan(x: float = numpy.nan, y: float = numpy.nan, z: float = numpy.nan) -> str"
+    if hasattr(m, "kw_func_float_nan"):
+        assert doc(m.kw_func_float_nan) == "kw_func_float_nan" \
+                                           "(x: float = numpy.nan, y: float = numpy.nan, z: float = numpy.nan) -> str"
     assert doc(m.args_function) == "args_function(*args) -> tuple"
     assert doc(m.args_kwargs_function) == "args_kwargs_function(*args, **kwargs) -> tuple"
     assert doc(m.KWClass.foo0) == \