[Ada] Use runtime from base compiler during stage1
gcc/ada/
* Make-generated.in: Add rule to copy runtime files needed
during stage1.
* raise.c: Remove obsolete symbols used during bootstrap.
* gcc-interface/Make-lang.in: Do not use libgnat sources during
stage1.
(GNAT_ADA_OBJS, GNATBIND_OBJS): Split in two parts, the common
part and the part only used outside of stage1.
(ADA_GENERATED_FILES): Add runtime files needed during bootstrap
when recent APIs are needed.
(ada/b_gnatb.adb): Remove prerequisite.
* gcc-interface/system.ads: Remove obsolete entries.