bug#51583: 29.0.50; cygw32 build break

[Kazuhiro Ito]

Cygw32 build fails on trunk.

$ ./configure --with-w32
$ make

(snip)
  CCLD     temacs.exe
/usr/lib/gcc/x86_64-pc-cygwin/10/../../../../x86_64-pc-cygwin/bin/ld: 
w32fns.o:w32fns.c:(.text+0xec1a): undefined reference to `w32_get_resource'
collect2: error: ld returned 1 exit status
make[1]: *** [Makefile:647: temacs.exe] Error 1
make[1]: Leaving directory '/dfs/f/build/cygwin64/emacs/src'
make: *** [Makefile:450: src] Error 2

w32_get_resource function is defined in w32.c, which is not compiled
on Cygwin buid.

-- 
Kazuhiro Ito