macOS ships ncursesw.pc but no libncursesw (wide support is in plain
libncurses), so PKG_CHECK_MODULES succeeded, WIDE_CURSES_LIBS was set to
-lncursesw -lpanelw -lformw unverified, and libUI_TUI_wide failed with
"library 'ncursesw' not found". It also kept the existing
wide-in-plain-ncurses fallback probe from running, since that only runs
when HAVE_WIDE_NCURSES=0.
Link-test the pkg-config result and clear HAVE_WIDE_NCURSES if it does
not link. configure regenerated with autoconf 2.71; diff is only this
block.
