* common/sh-exectool.c (struct copy_buffer): Add infrastructure for
copying between streams.
(copy_buffer_{init,shred,do_copy,flush}): New functions.
(sh_exec_tool_stream): Rework 'sh_exec_tool' to operate on streams.
(nop_free): New function.
(sh_exec_tool): Express this in terms of 'sh_exec_tool_stream'.
* common/sh-exectool.h (sh_exec_tool_stream): New prototype.
Signed-off-by: Justus Winter <justus@g10code.com>