RISC-V: Re-enable GCC+Rust builds

[Asuna Yang]

I noticed that GCC+Rust builds for RISC-V were disabled about a year 
ago, as discussed in
https://lore.kernel.org/all/20240917000848.720765-1-jmontleo@redhat.com/

I'm a bit lost here. What are the main obstacles to re-enabling GCC 
builds now?

Conor said:
 > Okay. Short term then is deny gcc + rust, longer term is allow it 
with the same caveats as the aforementioned mixed stuff.
"the same caveats" means detecting what specifically?

We have a RISC-V PWM driver being written in Rust. Currently, GCC being 
disabled for building the kernel with Rust for RISC-V is the primary 
blocker for including these drivers in RISC-V distros. Therefore, I'd 
like to push forward and contribute to the re-enabling of GCC builds. Is 
there a more detailed direction on what I can do here?

Thanks.