[trunk] Addition to subreg section of rtl.text.

[Paolo Bonzini]

> I think one reason is that allowing zero_extracts of multi-word modes is
> (like this subreg thing) a little hard to pin down.  What happens when
> WORDS_BIG_ENDIAN && !BYTES_BIG_ENDIAN

Unless I had my grep wrong, the only such machines to do this are PDP11 
and ARM with special flags (-mbig-endian -mwords-little-endian) that 
were "for backward compatibility with older versions of GCC" in 1999 [1].

So, is this special case worth keeping?

Paolo

[1] 
http://www.ecos.sourceware.org/ecos/docs-1.2.1/ref/gnupro-ref/arm/index.html