Cygwin: Use SDL_windowsdialog

Add "OR CYGWIN" to "WINDOWS" guards
Add "AND NOT CYGWIN" to "UNIX" guards

[sdl-ci-filter cygwin]
[sdl-ci-filter msys2-*]
[sdl-ci-filter msvc-*]
[sdl-ci-filter ngage]

CMakeLists.txt

@@ -3598,7 +3598,7 @@ if (SDL_DIALOG)
   if(ANDROID)
     sdl_sources(${SDL3_SOURCE_DIR}/src/dialog/android/SDL_androiddialog.c)
     set(HAVE_SDL_DIALOG TRUE)
-  elseif(UNIX AND NOT APPLE AND NOT RISCOS AND NOT HAIKU)
+  elseif(UNIX AND NOT (APPLE OR RISCOS OR HAIKU OR CYGWIN))
     sdl_sources(${SDL3_SOURCE_DIR}/src/dialog/unix/SDL_unixdialog.c)
     sdl_sources(${SDL3_SOURCE_DIR}/src/dialog/unix/SDL_portaldialog.c)
     sdl_sources(${SDL3_SOURCE_DIR}/src/dialog/unix/SDL_portaldialog.h)
@@ -3608,7 +3608,7 @@ if (SDL_DIALOG)
   elseif(HAIKU)
     sdl_sources(${SDL3_SOURCE_DIR}/src/dialog/haiku/SDL_haikudialog.cc)
     set(HAVE_SDL_DIALOG TRUE)
-  elseif(WINDOWS)
+  elseif(WINDOWS OR CYGWIN)
     sdl_sources(${SDL3_SOURCE_DIR}/src/dialog/windows/SDL_windowsdialog.c)
     set(HAVE_SDL_DIALOG TRUE)
   elseif(MACOS)
@@ -3616,7 +3616,7 @@ if (SDL_DIALOG)
     set(HAVE_SDL_DIALOG TRUE)
   endif()
 endif()
-if(UNIX AND NOT APPLE AND NOT RISCOS AND NOT HAIKU)
+if(UNIX AND NOT (APPLE OR RISCOS OR HAIKU OR CYGWIN))
   sdl_sources(${SDL3_SOURCE_DIR}/src/dialog/unix/SDL_zenitymessagebox.h)
   sdl_sources(${SDL3_SOURCE_DIR}/src/dialog/unix/SDL_zenitymessagebox.c)
 endif()