bug#74312: 31.0.50; Cygw32 build break

[Kazuhiro Ito <kzhr@d1.dion.ne.jp>]

Cygw32 build fails on  master

$ make
(snip)
  CC       w32fns.o
../../../emacs/src/w32fns.c: In function ‘process_dropfiles’:
../../../emacs/src/w32fns.c:2549:17: error: ‘MAX_UTF8_PATH’ undeclared (first use in this function); did you mean ‘MAX_ZONE_PATH’?
 2549 |   char filename[MAX_UTF8_PATH];
      |                 ^~~~~~~~~~~~~
      |                 MAX_ZONE_PATH
../../../emacs/src/w32fns.c:2549:17: note: each undeclared identifier is reported only once for each function it appears in
../../../emacs/src/w32fns.c:2557:11: warning: implicit declaration of function ‘filename_from_utf16’ [-Wimplicit-function-declaration]
 2557 |           filename_from_utf16 (p, filename);
      |           ^~~~~~~~~~~~~~~~~~~
../../../emacs/src/w32fns.c:2557:11: warning: nested extern declaration of ‘filename_from_utf16’ [-Wnested-externs]
../../../emacs/src/w32fns.c:2567:11: warning: implicit declaration of function ‘gifilename_from_ansi’ [-Wimplicit-function-declaration]
 2567 |           filename_from_ansi (p, filename);
      |           ^~~~~~~~~~~~~~~~~~
../../../emacs/src/w32fns.c:2567:11: warning: nested extern declaration of ‘filename_from_ansi’ [-Wnested-externs]
../../../emacs/src/w32fns.c:2549:8: warning: unused variable ‘filename’ [-Wunused-variable]
 2549 |   char filename[MAX_UTF8_PATH];
      |        ^~~~~~~~
make[2]: *** [Makefile:457: w32fns.o] Error 1


MAX_UTF8_PATH is defined in nt/inc/ms-w32.h and filename_from_*
functions are defined in src/w32.c


-- 
Kazuhiro Ito