When I was preparing to regression-test something else in a 
nios2-linux-gnu build, I discovered it was ICE'ing while building shared 
libraries with -fpic (glibc, libgomp).  I tracked this down to having 
started with r224048, but on further investigation I decided that commit 
merely exposed a latent bug.

The trouble is that the assertion in nios2_delegitimize_address is too 
restrictive compared to what nios2_legitimize_address can produce.  It's 
expecting to find a SYMBOL_REF underneath but in one case it was 
crashing on a LABEL_REF (for a computed goto), and in another case it 
was a symbol + offset expression which is even documented with a big 
block of comments in nios2_legitimize_address.  I've checked in this 
patch to relax the assertion; it allows the toolchain to build again, 
and test results look decent.

-Sandra