In ancient times, the existence of QMAKE_RUN_CXX_IMP determined the use of implicit rules. The code path for implicit rules was turned off in 2006 (0287fe3c), which probably was a refactoring artifact. Later, implicit rules were enabled again using a different approach. These days, the non-existence of QMAKE_RUN_CXX determines the use of implicit rules. We remove the dead code path now and rely on the latter condition. One part of the dead code is a feature that turns off inference rules if the OBJECTS_DIR is set or source file names do not match expectations. If somebody ever missed this, it has been reimplemented otherwise. Or not. Change-Id: If3ce9904d9c1df6e4048c58c2452854cce7fa206 Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>