Compile error on Cygwin due to `stdscr` macro conflict

[fd00]

environment

• ruby/curses: 1.5.3 (also reproducible on master)
• ncurses: 6.4

compiling curses.c
In file included from /usr/include/curses.h:90,
                 from curses.c:26:
curses.c:1699:11: error: field ‘ncwrap_stdscr’ declared as a function
 1699 |     VALUE stdscr;
      |           ^~~~~~
curses.c: In function ‘screen_initialize’:
curses.c:1780:21: error: lvalue required as left operand of assignment
 1780 |     screenp->stdscr = Qnil;
      |                     ^
curses.c: In function ‘screen_set_term’:
curses.c:1799:25: error: lvalue required as left operand of assignment
 1799 |         screenp->stdscr = prep_window(cWindow, stdscr, 1);
      |                         ^

On Cygwin, stdscr is defined as a macro in curses.h
(see: https://github.com/mirror/ncurses/blob/v6.4/include/curses.h.in#L1466).
This conflicts with the stdscr member in the struct screendata.

Would it be possible to rename the stdscr member in struct screendata to avoid the conflict?