Changes related to PR pybind#4285 (new style of warning suppression based on push/pop)

Author: rwgk

include/pybind11/detail/init.h

@@ -209,7 +209,7 @@ void construct(value_and_holder &v_h, std::unique_ptr<Cpp<Class>, D> &&unq_ptr,
     PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
     auto *ptr = unq_ptr.get();
     no_nullptr(ptr);
-    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr)) {
+    if (Class::has_alias && need_alias && !is_alias<Class>(ptr)) {
         throw type_error("pybind11::init(): construction failed: returned std::unique_ptr pointee "
                          "is not an alias instance");
     }
@@ -246,7 +246,7 @@ void construct(value_and_holder &v_h, std::shared_ptr<Cpp<Class>> &&shd_ptr, boo
     PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
     auto *ptr = shd_ptr.get();
     no_nullptr(ptr);
-    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr)) {
+    if (Class::has_alias && need_alias && !is_alias<Class>(ptr)) {
         throw type_error("pybind11::init(): construction failed: returned std::shared_ptr pointee "
                          "is not an alias instance");
     }

include/pybind11/stl.h

@@ -391,19 +391,15 @@ struct variant_caster<V<Ts...>> {
 
     template <typename U, typename... Us>
     bool load_alternative(handle src, bool convert, type_list<U, Us...>) {
-#if defined(__MINGW32__)
-#    pragma GCC diagnostic push
-#    pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
-#endif
+        PYBIND11_WARNING_PUSH
+        PYBIND11_WARNING_DISABLE_GCC("-Wmaybe-uninitialized")
         auto caster = make_caster<U>();
         if (caster.load(src, convert)) {
             value = cast_op<U>(std::move(caster));
             return true;
         }
         return load_alternative(src, convert, type_list<Us...>{});
-#if defined(__MINGW32__)
-#    pragma GCC diagnostic pop
-#endif
+        PYBIND11_WARNING_POP
     }
 
     bool load_alternative(handle, bool, type_list<>) { return false; }