(bib) libobjc build failure

[Nathanael Nerode]

>The immediate fix is probably going to be to add #includes of
>coretypes.h and tm.h to most of libobjc.  The _correct_ fix is to make
>libobjc find this stuff out some other way, but I'm not up for that
>right now.
>
>zw

I'm back to a successful build by including them *only* in encoding.c, 
the original problem file.  Think we can get away with that?

--Nathanael