[w7]

Yes, but at that point you've implemented abstractions on the JVM's abstractions, or used platform/implementation dependent code.

What's the point, just to say you did it?

It's not impossible, it's just not worth the ROI time wise for most people with the desire to make a C/C++ standard compliant compiler to do so-- and even if they do, the amount of traction it'll gain will be minimal because developers can make an educated choice not to use it when native C/C++ compilers are available, or alternative JVM languages like Kotlin.

Which is why you have a bunch of attempts at this that stopped development in 2009/2015.