The LibreSSL version in -current isn't explicitly supported.

Index: openssl-sys/build/main.rs
--- openssl-sys/build/main.rs.orig
+++ openssl-sys/build/main.rs
@@ -272,7 +272,7 @@ See rust-openssl documentation for more information:
             (3, 7, 0) => ('3', '7', '0'),
             (3, 7, 1) => ('3', '7', '1'),
             (3, 7, _) => ('3', '7', 'x'),
-            (3, 8, 0) => ('3', '8', '0'),
+            (3, 8, _) => ('3', '8', '0'),
             _ => version_error(),
         };