1) if gcc with --sys-root is used ./configure fails with: "gcc cannot compile ..." if the sys-root libc is a higher version than the host's
2) for any gcc that succeeds libreadline.so is built without lib(n)curses.so dependence which is mostly unimportant, but only mostly.
It came to my attention when building fontconfig package which fails with "UP undeclared ..." or such.
The way around these is:
configure as: CC=/usr/bin/gcc ./configure ...
sed -i 's:SHLIB_LIBS =:SHLIB_LIBS = -lncurses:' shlib/Makefile
unset CC
where gcc is the host compiler built without --sys-root
All the best