* cse.c (cse_insn): Call never_reached_warning when a jump is
changed to be unconditional.
* flags.h: Declare warn_notreached.
* flow.c (delete_block): Call never_reached_warning when
a block is deleted.
* jump.c (delete_barrier_successors): Call never_reached_warning
when we delete everything after a BARRIER.
(never_reached_warning): New function.
* rtl.h: Declare never_reached_warning.
* toplev.c (warn_notreached): New variable.
(lang_independent_options): Set warn_notreached
when -Wunreachable-code.
(compile_file): We need line numbers for -Wunreachable-code.

Also modify documentation to suit.

From-SVN: r28747