build: Fix ncursesw include lookup

Mirror what is already done for libffi; Look it up via
pkg-config and use the exported path via sysconfig in setup.py

Makefile.pre.in

@@ -355,6 +355,7 @@ IO_OBJS=	\
 ##########################################################################
 
 LIBFFI_INCLUDEDIR=	@LIBFFI_INCLUDEDIR@
+NCURSESW_INCLUDEDIR=	@NCURSESW_INCLUDEDIR@
 
 ##########################################################################
 # Parser

configure.ac

@@ -6410,10 +6410,17 @@ then
   [Define if you have struct stat.st_mtimensec])
 fi
 
+if test -n "$PKG_CONFIG"; then
+    NCURSESW_INCLUDEDIR="`"$PKG_CONFIG" ncursesw --cflags-only-I 2>/dev/null | sed -e 's/^-I//;s/ *$//'`"
+else
+    NCURSESW_INCLUDEDIR=""
+fi
+AC_SUBST(NCURSESW_INCLUDEDIR)
+
 # first curses header check
 ac_save_cppflags="$CPPFLAGS"
 if test "$cross_compiling" = no; then
-  CPPFLAGS="$CPPFLAGS -I/usr/include/ncursesw"
+  CPPFLAGS="$CPPFLAGS -I$NCURSESW_INCLUDEDIR"
 fi
 
 AC_CHECK_HEADERS(curses.h ncurses.h)

setup.py

@@ -1145,7 +1145,7 @@ def detect_readline_curses(self):
         if curses_library == 'ncursesw':
             curses_defines.append(('HAVE_NCURSESW', '1'))
             if not CROSS_COMPILING:
-                curses_includes.append('/usr/include/ncursesw')
+                curses_includes.append(sysconfig.get_config_var("NCURSESW_INCLUDEDIR"))
             # Bug 1464056: If _curses.so links with ncursesw,
             # _curses_panel.so must link with panelw.
             panel_library = 'panelw'