Enable C++20 and re-enable MSVC build

Also switched to standard-conforming __VA_OPT__ for logging.

src/core/inner_fat.h

@@ -23,7 +23,8 @@ struct ArchiveFormatInfo {
     u32_le number_files;       ///< The pre-defined number of files in the archive.
     u8 duplicate_data;         ///< Whether the archive should duplicate the data.
 };
-static_assert(std::is_pod<ArchiveFormatInfo>::value, "ArchiveFormatInfo is not POD");
+static_assert(std::is_standard_layout_v<ArchiveFormatInfo> && std::is_trivial_v<ArchiveFormatInfo>,
+              "ArchiveFormatInfo is not POD");
 
 union TableOffset {
     // This has different meanings for different savegame layouts