signal.c: get rid of system name

* signal.c (sighandler_t): get rid of clash with system provided name.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43156 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
io.c: suppress false uninitialized-variable warning

* io.c (io_ascii8bit_binmode): split from rb_io_ascii8bit_binmode() to
  call with rb_io_t* directly.

* io.c (copy_stream_body): move src_io and dst_io into each blocks
  where those are only used.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43157 b2dd03c8-39d4-4d8f-98ff-823fe69b080e