trans.c (gnat_to_gnu): Simplify expansion to use only a single check instead of three...
* gcc-interface/trans.c (gnat_to_gnu) <N_Slice>: Simplify expansion
to use only a single check instead of three, and avoid unnecessary
COMPOUND_EXPR.
(emit_check): Avoid useless COMPOUND_EXPRs and SAVE_EXPRs, sometimes
creating more opportunities for optimizations.