python3: stop forcing the ncursesw/{ncurses,panel}.h checks to "no"

python3: stop forcing the ncursesw/{ncurses,panel}.h checks to "no"

d883c02a4106 ("python3: pin host curses to the SDK's narrow ncurses",
2026-05-28) forced every curses header check Python's configure.ac
runs to "no", specifically to keep host ncurses's (then narrow-only)
build from being shadowed by whatever curses headers the build host's
own distro happened to ship under /usr/include.

That assumption broke when openwrt/openwrt@18725c45a33a ("ncurses:
bump to 6.6.20260801") switched host ncurses to track ncurses' git
snapshots rather than the old 6.4 tarball: ncurses 6.6+ defaults to
building wide-character support for ABI 6 (cf_dft_widec, gated on
cf_cv_abi_default which is just the major version - this is a policy
change accumulated in ncurses' own git history since 6.4 was tagged,
not something OpenWrt or ncurses deliberately changed for wide-char
specifically). Host ncurses now produces ncursesw.pc/panelw.pc, which
Python 3.14's configure.ac finds independently via its own
PKG_CHECK_MODULES(CURSES, ncursesw)-style pkg-config probe ("checking
for ncursesw... yes") - a check that was never gated by these ac_cv_*
overrides in the first place. That flips on the wide-character code
paths in Modules/_cursesmodule.c, while the ac_cv_header_ncursesw_*=no
overrides still force the *header* checks to fail, so the actual
#include falls through to the stale narrow ncurses/ncurses.h. The
result is a mismatch between what pkg-config says is available and
what header actually got included, producing:

  ./Modules/_cursesmodule.c: error: implicit declaration of function
  'unget_wch'; did you mean 'ungetch'?

(and similarly for wget_wch, wins_nwstr, mvwins_nwstr - every
wide-character-only curses function).

Fix this at the python3/ncurses integration boundary rather than by
touching ncurses' own host build behaviour globally (see
openwrt/openwrt#24811, which tried --disable-widec on host ncurses
and had to be reverted: it also drops extended colors from host tic,
shrinking MAX_ENTRY_SIZE 32768->4096 so tic can no longer process the
xterm/xterm-256color terminfo entries needed to assemble the target
terminfo package). Since host ncurses's own -I.../include/ncursesw
already gets added via pkg-config's Cflags substitution regardless of
these overrides, stop forcing ac_cv_header_ncursesw_{ncurses,panel}_h
to "no" - configure now genuinely finds ncursesw/ncurses.h in
staging_dir/hostpkg, consistent with what its own pkg-config check
already reports, and both detection paths agree.

ac_cv_header_ncursesw_curses_h stays forced, along with the bare
(non-w) curses.h/ncurses.h/panel.h checks: host ncurses is configured
with --without-curses-h, so staging_dir/hostpkg/include/ncursesw/ has
no curses.h of its own to genuinely detect - a real "yes" here could
only ever come from the build host's own /usr/include/ncursesw/
curses.h (e.g. Fedora's ncurses-devel), the exact distro-shadowing
this override block exists to prevent.

Verified end to end: clean host python3 rebuild against unmodified
current ncurses compiles Modules/_cursesmodule.c and
Modules/_curses_panel.c without error, and the resulting
staging_dir/hostpkg python3.14 successfully `import curses` with
unget_wch present.

Fixes: d883c02a4106 ("python3: pin host curses to the SDK's narrow ncurses")
Signed-off-by: Daniel Golle <redacted>