Make DESTDIR operation match common practice
Modify DESTDIR to match common practice (for instance, that of automake), in that DESTDIR represents a staged install directory. It is intended that the tree would need to than be copied to the final install location afterwards. When supplied, DESTDIR will not change any compiled-in paths in darshan.
See the automake manual section about DESTDIR for an example of standard usage.
https://www.gnu.org/software/automake/manual/html_node/DESTDIR.html