Make bitfields example runnable when `run.dlang.org` has dmd 2.112

[ntrel]

Change awaiting run.dlang.org update:
https://github.com/dlang/dlang.org/compare/master...ntrel:dlang.org:bitfields-ex?expand=1

[ntrel]

Note: That currently requires Initializer support too, which would be 2.113.