Add f16 and f128 configuration from compiler-builtins

In preparation of adding routines from these two types, duplicate the
`compiler-builtins` configuration here.

library/compiler-builtins/libm/crates/libm-macros/Cargo.toml

@@ -12,3 +12,10 @@ heck = "0.5.0"
 proc-macro2 = "1.0.88"
 quote = "1.0.37"
 syn = { version = "2.0.79", features = ["full", "extra-traits", "visit-mut"] }
+
+[lints.rust]
+# Values used during testing
+unexpected_cfgs = { level = "warn", check-cfg = [
+  'cfg(f16_enabled)',
+  'cfg(f128_enabled)',
+] }