Do not call openssl_probe::init_ssl_cert_env_vars() on FreeBSD (rust-lang#1129)

The heuristics in openssl-probe leave the process environment with an invalid
value breaking the certificate validation on FreeBSD. FreeBSD has a system
truststore managed by certctl(8). Leave it to OpenSSL to do the right thing.

Upstream issue: alexcrichton/openssl-probe#37

This fixes rust-lang#1129

Author: michael-o

src/lib.rs

@@ -759,6 +759,7 @@ fn init() {
     unix,
     not(target_os = "macos"),
     not(target_os = "ios"),
+    not(target_os = "freebsd"),
     feature = "https"
 ))]
 fn openssl_env_init() {
@@ -880,6 +881,7 @@ fn openssl_env_init() {
     windows,
     target_os = "macos",
     target_os = "ios",
+    target_os = "freebsd",
     not(feature = "https")
 ))]
 fn openssl_env_init() {}