libc-test: add allowlist for positive s! marco configs

Namely, this allows `target_endian` as well as adds a constant array
where certain configs are explicitly allowed (e.g. musl32_time64).

Author: xbjfk

libc-test/tests/style_lib/mod.rs

@@ -38,6 +38,7 @@ use syn::visit::{self, Visit};
 use syn::Token;
 
 const ALLOWED_REPEATED_MACROS: &[&str] = &["s", "s_no_extra_traits", "s_paren"];
+const ALLOWED_POSITIVE_S_CFGS: &[&str] = &["gnu_file_offset_bits64", "gnu_time_bits64", "musl32_time64", "musl_v1_2_3"];
 
 pub type Error = Box<dyn std::error::Error>;
 pub type Result<T> = std::result::Result<T, Error>;
@@ -272,6 +273,8 @@ impl StyleChecker {
                 if !meta_str.starts_with("not")
                     && !meta_str.starts_with("any")
                     && !meta_str.starts_with("all")
+                    && !meta_str.starts_with("target_endian")
+                    && !ALLOWED_POSITIVE_S_CFGS.contains(&meta_str.as_str())
                 {
                     self.error(
                         "positive #[cfg] for s! macro".to_string(),