Unused Argument Warnings in Intrinsics Without Body

[vayunbiyani]

Problem:
The compiler emits warnings about unused arguments in intrinsic functions without bodies (when #[rustc_intrinsic] is used). These arguments are inherently unused, but the warnings create unnecessary noise.

Proposed Solution:
Update the compiler to automatically suppress unused argument warnings for intrinsics without bodies. This eliminates the need for manual workarounds like prefixing variable names with _.

Issue reproduced here:
#135333 (comment)

[RalfJung]

Cc @oli-obk

[cyrgani]

@rustbot label -I-ICE

[vayunbiyani]

@rustbot claim