bug#71786: 30.0.60; Compiler warnings in the Cygwin-w32 build

[Ken Brown <kbrown@cornell.edu>]

The following warnings occur in the Cygwin-w32 build, on both the
emacs-30 and the master branch:

../../src/w32fns.c: At top level:
../../src/w32fns.c:10581:1: warning: no previous prototype for ‘w32_get_resource’ 
[-Wmissing-prototypes]
10581 | w32_get_resource (const char *key, const char *name, LPDWORD lpdwtype)
       | ^~~~~~~~~~~~~~~~
../../src/w32fns.c:11288: warning: macro "DEFAULT_IMAGE_BASE" is not used [-Wunused-macros]
11288 | # define DEFAULT_IMAGE_BASE (ptrdiff_t)0x01000000
       |

This fixes them on both branches:

diff --git a/src/cygw32.h b/src/cygw32.h
index cc3414a39d92..2f265cab4adf 100644
--- a/src/cygw32.h
+++ b/src/cygw32.h
@@ -35,5 +35,6 @@ #define CYGW32_H

  extern void syms_of_cygw32 (void);
  extern char * w32_strerror (int error_no);
+extern LPBYTE w32_get_resource (const char * key, const char * name, LPDWORD type);

  #endif /* CYGW32_H */
diff --git a/src/w32fns.c b/src/w32fns.c
index b784a9a563d7..4c2f18abd084 100644
--- a/src/w32fns.c
+++ b/src/w32fns.c
@@ -11284,7 +11284,7 @@ #define BACKTRACE_LIMIT_MAX 62
     configure.ac.  */
  #if defined MINGW_W64 && EMACS_INT_MAX > LONG_MAX
  # define DEFAULT_IMAGE_BASE (ptrdiff_t)0x400000000
-#else  /* 32-bit MinGW build */
+#elif !defined CYGWIN  /* 32-bit MinGW build */
  # define DEFAULT_IMAGE_BASE (ptrdiff_t)0x01000000
  #endif

OK for the emacs-30 branch?

Ken