Set max_jobs for 'native.recommended'

mx.fastr/suite.py

@@ -331,6 +331,7 @@ suite = {
         "com.oracle.truffle.r.engine",
         "com.oracle.truffle.r.ffi.impl"
       ],
+      "max_jobs" : 8,
       "native" : True,
       "workingSets" : "FastR",
       "buildDependencies" : ["FASTR"],