Comment 2 for bug 2070284

To illustrate my point from the previous comment, this patch fixes the build in oracular, but I'm unsure if it's the correct fix, given that it build fine about 2 months ago and gnu17 was still the standard used back then:
--- a/meson.build
+++ b/meson.build
@@ -5,8 +5,8 @@ project('dia',
         default_options: [
                              'warning_level=1',
                              'buildtype=debugoptimized',
- 'c_std=gnu17',
- 'cpp_std=gnu++17',
+ 'c_std=gnu2x',
+ 'cpp_std=gnu++20',
                          ],
 )