This patch is taken from:
http://cvs.savannah.gnu.org/viewvc/make/main.c?root=make&r1=1.246&r2=1.247

When we re-exec the master makefile in a jobserver environment, ensure
that MAKEFLAGS is set properly so the re-exec'd make runs in parallel.
See Savannah bug #33873.

bug #33873: MAKEFLAGS=-jN gets lost on reexec
https://savannah.gnu.org/bugs/?33873

sr #107487: MAKEFLAGS not being honored always (regression) in 3.82
https://savannah.gnu.org/support/index.php?107487

--- a/main.c	2010/08/29 23:05:27	1.246
+++ b/main.c	2011/09/18 23:39:26	1.247
@@ -2088,6 +2088,11 @@
 
           ++restarts;
 
+          /* If we're re-exec'ing the first make, put back the number of
+             job slots so define_makefiles() will get it right.  */
+          if (master_job_slots)
+            job_slots = master_job_slots;
+
           /* Reset makeflags in case they were changed.  */
           {
             const char *pv = define_makeflags (1, 1);
@@ -2824,9 +2829,6 @@
 		       && (*(unsigned int *) cs->value_ptr ==
 			   *(unsigned int *) cs->noarg_value))
 		ADD_FLAG ("", 0); /* Optional value omitted; see below.  */
-	      else if (cs->c == 'j')
-		/* Special case for `-j'.  */
-		ADD_FLAG ("1", 1);
 	      else
 		{
 		  char *buf = alloca (30);