Fuzz multiple targets in cranelift-icache (#5482)

Fuzz additional targets in the cranelift-icache target. The list of targets fuzzed is controlled by the targets enabled in fuzz/Cargo.toml.

This PR also reworks how instruction disabling is done in function generator, moving the deny-list to a function to make the decision at runtime instead of compile time.

cranelift/fuzzgen/Cargo.toml

@@ -16,3 +16,4 @@ cranelift-native = { workspace = true }
 
 anyhow = { workspace = true }
 arbitrary = "1.0.0"
+target-lexicon = { workspace = true, features = ["std"] }