Whitelist known cfgs

Rust is now checking cfg attributes for typos but this interferes with
our cfgs that rustc/cargo don't recognize. This whitelists them so they
no longer produce warnings.

This is a backport of 614fe81 because the warnings make development
very annoying.

Cargo.toml

@@ -54,6 +54,8 @@ bincode = "1.3.3"
 wasm-bindgen-test = "0.3"
 getrandom = { version = "0.2", features = ["js"] }
 
+[lints.rust]
+unexpected_cfgs = { level = "deny", check-cfg = ['cfg(bench)', 'cfg(secp256k1_fuzz)', 'cfg(rust_secp_no_symbol_renaming)'] }
 
 [[example]]
 name = "sign_verify_recovery"

secp256k1-sys/Cargo.toml

@@ -32,3 +32,6 @@ recovery = []
 lowmemory = []
 std = ["alloc"]
 alloc = []
+
+[lints.rust]
+unexpected_cfgs = { level = "deny", check-cfg = ['cfg(bench)', 'cfg(secp256k1_fuzz)', 'cfg(rust_secp_no_symbol_renaming)'] }