debug build (using -g and disabling all -O options), but also sets a whole
range of picky/strict compiler options depending on what compiler and version
that is used. This function is ripped right off the curl configure script,
written by yours truly. I left it using the same name as in the curl script
to 1) make it obvious where it comes from, so that 2) it will be easier to
update and keep it in sync with future modifications.
Now, this shows MAAAAAAAAANY warnings...
