with-camlibs: document "everything" set in the --help output
with-camlibs: document "everything" set in the --help output

As configuring --with-camlibs=everything is a very valid option
for build tests, document it.

gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2