Vector shifting patch

[Dominique Dhumieres]

On x86_64-apple-darwin10.4.0, compiling gcc.dg/torture/vector-shift2.c 
with -O3 -g gives an ICE:

[macbook] f90/bug% gcc46 /opt/gcc/work/gcc/testsuite/gcc.dg/torture/vector-shift2.c  -O3 -g
/opt/gcc/work/gcc/testsuite/gcc.dg/torture/vector-shift2.c: In function 'main':
/opt/gcc/work/gcc/testsuite/gcc.dg/torture/vector-shift2.c:59:1: internal compiler error: in simplify_subreg, at simplify-rtx.c:5217

with both -m32 and -m64.

TIA

Dominique