https://github.com/sfackler/rust-openssl/pull/2287

Index: vendor/openssl-sys-0.9.102/src/handwritten/conf.rs
--- vendor/openssl-sys-0.9.102/src/handwritten/conf.rs.orig
+++ vendor/openssl-sys-0.9.102/src/handwritten/conf.rs
@@ -1,7 +1,13 @@
 use super::super::*;
 
+const_ptr_api! {
+    extern "C" {
+        pub fn NCONF_new(meth: #[const_ptr_if(libressl400)] CONF_METHOD) -> *mut CONF;
+    }
+}
+
 extern "C" {
-    pub fn NCONF_new(meth: *mut CONF_METHOD) -> *mut CONF;
+    #[cfg(not(libressl400))]
     pub fn NCONF_default() -> *mut CONF_METHOD;
     pub fn NCONF_free(conf: *mut CONF);
 }
