Using MAKE_RESTARTS as indicator whether to source environment.
'make foo -o bar' should work again.

Change-Id: I6086b661559b39897f1d5378919541fb786bdf0e
Reviewed-on: https://gerrit.libreoffice.org/1478Reviewed-by: Peter Foley <pefoley2@verizon.net>
Tested-by: Peter Foley <pefoley2@verizon.net>