daemon: Remove separate configure of daemon subdirectory.

Combine the two Gnulib instances together.

Add checks from old daemon/configure.ac into configure.ac.

Fix daemon/Makefile.am so it is like a normal subdirectory
Makefile.am.

Because we are now using the replacement strerror_r function from
Gnulib (instead of the one from glibc directly), this requires a small
change to src/guestfs.c.