Fix bsd cmake build failure

[mmyjona]

Summary

Build "Fix netbsd ncurses build. The ncurses include path is set with CURSES_INCLUDE_DIRS"

Purpose of change

Fix build error when build the ncurse version under *bsd.

1. The ncurses and ncursesw installed with pkgsrc can be detected with cmake but it should be set in the imtui cmake file explicitly.
2. The backtrace feature relies on libexecinfo to work properly.

Testing

Pull the code and build it under linux and *bsd.