Low: build: Check for NCURSES_CONST macro definition

We use it in crm_mon_curses.c, but we've never checked for it at build
time. Instead, we've always tried to use regular curses (non-ncurses) if
ncurses is not available. NCURSES_CONST won't be defined there.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>

Author: nrwahl2

configure.ac

@@ -1348,7 +1348,7 @@ AS_IF([test $found_curses -eq 1 && cc_supports_flag -Wcast-qual], [
                 #include PCMK__CURSES_H
                 #endif
             ],
-            [printw((const char *) "Test");]
+            [printw((NCURSES_CONST char *) "Test");]
         )],
         [AC_MSG_RESULT([yes])
          PCMK_FEATURES="$PCMK_FEATURES ncurses"