Indeed!
Very often, the price you pay for greater efficiency is reduced portability.
I was just pointing out the pros & cons of the 2 approaches.

Even the union need not be a show-stopper for portability; if you write carefully, and isolate all your compiler/target dependencies into one place, it's not so bad to have compiler/target-specific versions of that file.
You can use #if to select the appropriate version, and then the rest of the code just keeps using the same names!