[m32c] structure returns and stack debug info

[DJ Delorie]

> Would this be material you could add to gcc-4.2/changes.html?

Only if "Changes" is appropriate for *bugfixes* that break
compatibility.  The ABI as published isn't changing, I'm just fixing a
bug in implementing it.

I've been making a ton of changes in m32c-land, although this is the
first that that I know of that requires rebuilding libraries, and only
those libraries that have functions which return structures.  Although
people are using the m32c port, it's still kinda "new" and thus is
still settling.