Fix a regression introduced in svn r10344 in autoconf/configure builds.

Shared library sizes were about 4x the usual size, because makeinclude
and fltk-config always used "-g -O2", i.e. debugging compiler options.


git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10403 ea41ed52-d2ee-0310-a9c1-e6b18d33e121