`grep' command on MS Windows with Cygwin, looking for text with Unicode chars

[Drew Adams]

Is there a simple way to use `M-x grep' (e.g., giving it
some switches or escape chars or replacing them with hex
escapes or...) to search for some text that includes
non-ASCII Unicode chars?

[I'm using (an old) Cygwin `grep'.  Dunno whether that
matters.]

I tried to look for "'%s'" (curly-quote) in the Emacs
source code.

E.g., in `info.el' we now have this:
(format "Index for '%s'" string) instead of this:
(format "Index for `%s'" string)

I wanted to see if this kind of change was spread to
other files.

I tried things like "\\x2018%s\\x2019", with no luck.
Is there a simple approach that uses only `M-x grep'
and not, say, piping the result of iconv to grep?

I ended up doing the search using Icicles, but I'd
like to be able to do such a search also using
just `grep' (or `rgrep' etc.).