#4 Fix Makefile remake targets

[Ronald Landheer-Cieslak]

Fix targets for remaking configure.ac from
configure.ac.in; configure from configure.ac;
Makefile.in from Makefile.in.in; Makefile from
Makefile.in; link.mk
I.e.: Makefile.in, configure, configure.ac and link.mk
should be re-made if bootstrap is newer or any of their
direct decendants is newer and Makefile should be
re-made if configure is newer or Makefile.in.in is
newer (note that configure also makes config.status