radv: allow to create a noop FS in a library with GPL
Alternative solution for !21015 (closed) because NIR linking in RADV should be adjusted but it's really tricky. Basically, the driver would need to make a difference between 1) I'm in a lib and the FS stage is unknown (varyings shouldn't be removed) vs 2) I'm in a pipeline and it's a noop FS (varyings should be removed).
Edited by Samuel Pitoiset