Add support for WinCE toolchains

[Stan Shebs]

DJ Delorie wrote:
> 
> > This should get a special mention in gdb/NEWS, and ideally in README
> > also; this is one of those situations where you'll be glad you
> > forestalled a slew of complaints and bug reports by documenting it
> > in several places.
> 
> Is it acceptable to add notes to configure, so that if you said
> "./configure --target=arm-pe" it could print out "Note: if you wanted
> Windows CE, use arm-wince-pe instead" ?  Maybe in the toplevel configure?

My kneejerk is to be unenthusiastic, although I'm not sure why.  I guess it
seems to me that notes in configure should be more about issues that are
more directly related to the configure script, while in this case (IIRC) the
differences are more in the sources.  But that's a pretty weak theoretical
argument, and if the extra warning sets even one user on the path of rightness,
then it's worthwhile to add.

Stan