wafsamba: Fix 'make -j<jobs>'

wafsamba: Fix 'make -j<jobs>'

Currently only 'make -j' enables parallel builds and e.g. 'make -j4'
results in no parallel compile jobs at all.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13606

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Alexander Bokovoy <ab@samba.org>
Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Fri Sep  7 20:24:46 CEST 2018 on sn-devel-144

(cherry picked from commit 70169d4789fe8b2ee4efe5e88eeaa80e1a641b32)

Autobuild-User(v4-8-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-8-test): Mon Sep 10 16:45:04 CEST 2018 on sn-devel-144