Need to bump MAXJOBS to 256.

Having to move to larger smp clusters so need more build
parallelism.

src/engine/jam.h

@@ -409,7 +409,7 @@
 #define MAXSYM   1024  /* longest symbol in the environment */
 #define MAXJPATH 1024  /* longest filename */
 
-#define MAXJOBS  64    /* internally enforced -j limit */
+#define MAXJOBS  256   /* internally enforced -j limit */
 #define MAXARGC  32    /* words in $(JAMSHELL) */
 
 /* Jam private definitions below. */