build(Windows): fix redoing version generation (#21880)

Problem: On Windows, neovim's version is generated every time nvim is
built, even if code hasn't been changed.  That is because version
generation is done based on a hash matching of a file and the content of
the file.  And in Windows they don't match, because of the DOS
line-endings.

Solution: Write the file containing nvim version with UNIX line-endings.

cmake/GenerateVersion.cmake

@@ -33,4 +33,7 @@ endif()
 if(NOT "${NVIM_VERSION_HASH}" STREQUAL "${CURRENT_VERSION_HASH}")
   message(STATUS "Using NVIM_VERSION: ${NVIM_VERSION}")
   file(WRITE "${OUTPUT}" "${NVIM_VERSION_STRING}")
+  if(WIN32)
+    configure_file("${OUTPUT}" "${OUTPUT}" NEWLINE_STYLE UNIX)
+  endif()
 endif()