Add C++ settings in the Linux config targets

Reviewed-by: NRich Salz <rsalz@openssl.org>

Configurations/10-main.conf

@@ -622,6 +622,7 @@ sub vms_info {
     "linux-generic32" => {
         inherit_from     => [ "BASE_unix" ],
         cc               => "gcc",
+        cxx              => "g++",
         cflags           => combine(picker(default => "-Wall",
                                            debug   => "-O0 -g",
                                            release => "-O3"),