Avoid LNK2001 in c++20 when /GL (Whole program optimization) is on with MSVC

Author: hellokenlee

include/pybind11/pybind11.h

@@ -43,6 +43,12 @@ PYBIND11_WARNING_DISABLE_CLANG("-Wgnu-zero-variadic-macro-arguments")
 #    include <cxxabi.h>
 #endif
 
+#if defined(__cpp_if_constexpr) && __cpp_if_constexpr >= 201606
+    #define PYBIND11_MYABE_CONSTEXPR constexpr
+#else
+    #define PYBIND11_MYABE_CONSTEXPR
+#endif
+
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
 /* https://stackoverflow.com/questions/46798456/handling-gccs-noexcept-type-warning
@@ -3606,7 +3612,8 @@ function get_override(const T *this_ptr, const char *name) {
             auto o = override(__VA_ARGS__);                                                       \
             PYBIND11_WARNING_PUSH                                                                 \
             PYBIND11_WARNING_DISABLE_MSVC(4127)                                                   \
-            if (pybind11::detail::cast_is_temporary_value_reference<ret_type>::value              \
+            if PYBIND11_MYABE_CONSTEXPR                                                           \
+                (pybind11::detail::cast_is_temporary_value_reference<ret_type>::value             \
                 && !pybind11::detail::is_same_ignoring_cvref<ret_type, PyObject *>::value) {      \
                 static pybind11::detail::override_caster_t<ret_type> caster;                      \
                 return pybind11::detail::cast_ref<ret_type>(std::move(o), caster);                \