Respect osslconf in systest

Also cfg off SSLv3_method, since it's disabled in the OpenSSL that ships
with Arch Linux. More such flags can be added on demand - it doesn't
seem worth auditing everything for them.

openssl-sys/build.rs

@@ -283,6 +283,7 @@ The build is now aborting due to this version mismatch.
 
         // Look for `#define OPENSSL_FOO`, print out everything as our own
         // #[cfg] flag.
+        let mut vars = vec![];
         for line in conf_header.lines() {
             let i = match line.find("define ") {
                 Some(i) => i,
@@ -291,8 +292,10 @@ The build is now aborting due to this version mismatch.
             let var = line[i + "define ".len()..].trim();
             if var.starts_with("OPENSSL") && !var.contains(" ") {
                 println!("cargo:rustc-cfg=osslconf=\"{}\"", var);
+                vars.push(var);
             }
         }
+        println!("cargo:osslconf={}", vars.join(","));
     }
 
     return version_text.to_string()

openssl-sys/src/ossl10x.rs

@@ -549,6 +549,7 @@ extern {
     pub fn OPENSSL_add_all_algorithms_noconf();
     pub fn HMAC_CTX_init(ctx: *mut ::HMAC_CTX);
     pub fn HMAC_CTX_cleanup(ctx: *mut ::HMAC_CTX);
+    #[cfg(not(osslconf = "OPENSSL_NO_SSL3_METHOD"))]
     pub fn SSLv3_method() -> *const ::SSL_METHOD;
     pub fn TLSv1_method() -> *const ::SSL_METHOD;
     pub fn SSLv23_method() -> *const ::SSL_METHOD;

systest/build.rs

@@ -31,6 +31,11 @@ fn main() {
     if env::var("DEP_OPENSSL_IS_110").is_ok() {
         cfg.cfg("ossl110", None);
     }
+    if let Ok(vars) = env::var("DEP_OPENSSL_OSSLCONF") {
+        for var in vars.split(",") {
+            cfg.cfg("osslconf", Some(var));
+        }
+    }
 
     cfg.header("openssl/comp.h")
        .header("openssl/dh.h")