Comment by sluongng

I suspect they just use no_std whenever its applicable

https://github.com/facebook/buck2/commit/4a1ccdd36e0de0b69ee...

https://github.com/facebook/buck2/commit/bee72b29bc9b67b59ba...

Turn out if you have strong control over the compiler and linker instrumentations, there are a lot of ways to optimize binary size