These configure flags enable code profiling (with gprof) and code
coverage (with gcov) respectively.
Although this is a nice idea, it's not currently very useful.
Libtool mangles filenames in such a way that gcov cannot locate its
datafiles.
Profiling is of dubious utility with libguestfs which is not CPU-bound
and relies extensively on running external programs (oprofile-like
system profiling that took into account libguestfs + qemu or
libguestfs + qemu + the appliance + filesystem tools *would* be
useful).
Also neither flag will help in capturing data from the appliance.