bug#41646: Startup in Windows is very slow when load-path contains many

[Lin Sun]

How about this: I write some windows specific code only available on
the windows to cache the files for the load-path. It will NOT affect
other platforms. Like a flag "load-path-cache-expired 60" (nil/t) for
windows users who won't change path/files a lot, then Emacs can cache
the files list for path entries for 60 seconds.  As I pasted, with the
files cache, it can reduce the startup time from ~16s to ~5s, and also
improve the running time performance. That will save a lot of emacs
windows users.