Fix weak-crypto feature (alexcrichton#152)

These flags are disabled by default at least in newer versions of openssl.
So They have to be explicitly enabled to be used.

Co-authored-by: Yuchen Wu <yuchen@cloudflare.com>

Author: james58899

src/lib.rs

@@ -165,7 +165,12 @@ impl Build {
             .arg("no-zlib")
             .arg("no-zlib-dynamic");
 
-        if cfg!(not(feature = "weak-crypto")) {
+        if cfg!(feature = "weak-crypto") {
+            configure
+                .arg("enable-md2")
+                .arg("enable-rc5")
+                .arg("enable-weak-ssl-ciphers");
+        } else {
             configure
                 .arg("no-md2")
                 .arg("no-rc5")