build: Check curses "bool" type compatibility

curses.h may define its own "bool" type, because the X/Open Curses
standard defines "bool" that predates C99 "bool". If curses.h "bool" is
not compatible with ISO C, fail at configure time.

(The C23 standard now makes "bool" a keyword so that a
"typedef /*whatever*/ bool;" is no longer portable. This is a bug that
curses implementations should fix.)

Solaris 11 is known to ship with a broken curses.h header (the default
curses, not ncurses).

Signed-off-by: Kang-Che Sung <explorer09@gmail.com>

configure.ac

@@ -696,9 +696,12 @@ CFLAGS="-I$srcdir $CFLAGS"
 # "stdscr" is a macro in ncursest (reentrant version of ncurses).
 AC_MSG_CHECKING([whether the curses header works])
 AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+/* Checks if the "bool" definition in curses is ISO C compatible */
+#include <stdbool.h>
+
 #include "ProvideCurses.h"
    ]], [[
-keypad(stdscr, 0);
+keypad(stdscr, false);
 
 refresh();