Use base make step for autotools projects

Unify generic and autotools make steps, by moving the better maintained
logic from the generic make step to the base make step.

Add fallback code for restoring settings from previous autotools make
steps, since a key was named slightly different.

The autotools make step was behaving a little bit better when there is
no C++ toolchain set in the kit, but on the other hand would just take
the make command from a random existing toolchain, which can be wrong
too. Anyhow, this must be fixed in a follow-up patch for all make steps.

Change-Id: I47af7d327feb9336790d30c8b9a4968c25b25db3
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/genericprojectmanager/genericmakestep.h

@@ -38,8 +38,6 @@ class GenericMakeStep : public ProjectExplorer::MakeStep
 
 public:
     explicit GenericMakeStep(ProjectExplorer::BuildStepList *parent, const QString &buildTarget = {});
-
-    bool init(QList<const BuildStep *> &earlierSteps) override;
 };
 
 class GenericMakeAllStepFactory : public ProjectExplorer::BuildStepFactory