merge auto_vec and stack_vec

gcc/ChangeLog

gcc/ada/ChangeLog

gcc/ada/gcc-interface/decl.c

gcc/config/i386/i386.c

gcc/cp/ChangeLog

gcc/cp/semantics.c

gcc/df-scan.c

gcc/function.c

gcc/genautomata.c

gcc/gimplify.c

gcc/graphite-clast-to-gimple.c

gcc/graphite-dependences.c

gcc/graphite-scop-detection.c

gcc/graphite-sese-to-poly.c

gcc/hw-doloop.c

gcc/trans-mem.c

gcc/tree-call-cdce.c

gcc/tree-data-ref.c

gcc/tree-dfa.c

gcc/tree-if-conv.c