Configure --openssldir to its default location (#141)

As pointed out in #140 otherwise certificates and configure is by
default looked up in the directory of the build machine itself which is
often a writable path. Instead switch the configuration option back to
the default recommended in openssl's `INSTALL.md`

Closes #140

src/lib.rs

@@ -134,12 +134,23 @@ impl Build {
             env::var("OPENSSL_SRC_PERL").unwrap_or(env::var("PERL").unwrap_or("perl".to_string()));
         let mut configure = Command::new(perl_program);
         configure.arg("./Configure");
+
+        // Change the install directory to happen inside of the build directory.
         if host.contains("pc-windows-gnu") {
             configure.arg(&format!("--prefix={}", sanitize_sh(&install_dir)));
         } else {
             configure.arg(&format!("--prefix={}", install_dir.display()));
         }
 
+        // Specify that openssl directory where things are loaded at runtime is
+        // not inside our build directory. Instead this should be located in the
+        // default locations of the OpenSSL build scripts.
+        if target.contains("windows") {
+            configure.arg("--openssldir=SYS$MANAGER:[OPENSSL]");
+        } else {
+            configure.arg("--openssldir=/usr/local/ssl");
+        }
+
         configure
             // No shared objects, we just want static libraries
             .arg("no-dso")