Always pass -j to cargo

https://cvsweb.openbsd.org/cgi-bin/cvsweb/ports/lang/rust/patches/patch-src_bootstrap_builder_rs.diff?r1=1.3&r2=1.4

--- src/bootstrap/builder.rs.orig	2018-05-07 17:31:28 UTC
+++ src/bootstrap/builder.rs
@@ -534,11 +534,7 @@ impl<'a> Builder<'a> {
              .arg("--target")
              .arg(target);
 
-        // If we were invoked from `make` then that's already got a jobserver
-        // set up for us so no need to tell Cargo about jobs all over again.
-        if env::var_os("MAKEFLAGS").is_none() && env::var_os("MFLAGS").is_none() {
-             cargo.arg("-j").arg(self.jobs().to_string());
-        }
+        cargo.arg("-j").arg(self.jobs().to_string());
 
         // FIXME: Temporary fix for https://github.com/rust-lang/cargo/issues/3005
         // Force cargo to output binaries with disambiguating hashes in the name