graph: Fix the build with slibtool.
When building freetype-demos with slibtool (https://dev.midipix.org/cross/slibtool) the build fails.
slibtool: error: output file prefix does not match its (archive) suffix; the expected prefix was 'lib'This is because the build graph suffix is incorrectly set to .a instead of .la and -module is missing. Making these two changes fixes the problem. GNU libtool did not expose this problem because it is overly permissive and doesn't follow their own documentation.
Also see this downstream issue.