The core linenoise code was being backported, but not
the README or example. It's less confusing for users
if everything matches across directories.
Fix inspired by @thrig
Closes#1872
Remove unused variables. Instead of overriding non-standard variables
such as ARCH and PROF, use standard variables CFLAGS and LDFLAGS to
override Makefile settings. Move dependencies generated by `make dep` to
a separate file.
