New ICE in optimize_mode_switching

[Richard Kenner]

This appeared with something checked in within the last 24 hours.

I verified that it was *not* the change to lcm.c that caused it.  I'll
investigate further, but does anybody have any ideas?

../../xgcc -B../../ -c -g -O2      -W -Wall -gnatpg  a-nllcef.ads -o a-nllcef.o
+===========================GNAT BUG DETECTED==============================+
| 5.03h (20040831) (x86_64-unknown-linux-gnu) GCC error:                   |
| in optimize_mode_switching, at lcm.c:1220                                |