"Everybody was dreaming of this commit log:
- factorization of makefiles for libCGAL, libCGALimageIO, libCore, and
libBenchmark.
- SONAMEs for everybody."
Add:
- fix platforms without SONAME,
- unify Benchmark/src/Benchmark/makefile with other makefiles.
This required to pass CXXFLAGS on the make command-line, and therefore
I took this opportunity to also pass CGAL_MAKEFILE on the command-line,
which in turn allowed to get rid of the prepare_lib_makefiles function.