Move configuration of global headers

Move configuration of global headers

Previously it was possible to get a different result from
  cmake .. && make && make install
than one got from
  cmake .. && cmake .. && make && make install
because the lmfit detection ran after config.h was generated,
so HAVE_LMFIT changed value from one cmake to the next, triggering
a rebuild of all source files that depended on config.h. lmfit
is supposed to fall back on the internal version, but did not,
so this is buggy. It's also very inefficient with compilation
in some workflows.