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);