Add "optforfuzzing" func attribute when fuzzing is enabled

[gnavdev28]

Description

This PR addresses issue #3172.
It ensures that the optforfuzzing LLVM attribute is added to functions when fuzzing is enabled. This behavior matches Clang's implementation and helps the LLVM optimizer work better for fuzzing targets.

Changes

• gen/functions.cpp: Added a check to see if fuzzing is enabled and then applied the OptForFuzzing attribute to the function.

Verification

I have verified this change by checking the generated LLVM IR (.ll file). The attribute is now correctly added to the functions.

Evidence from LLVM IR:

; Function Attrs: optforfuzzing uwtable
define void @_Dmain() #0 {
...
attributes #0 = { optforfuzzing ... }

[JohanEngelen]

lgtm, maybe add a testcase for it?

[gnavdev28]

@JohanEngelen do I need to fix the error bot?