dh-exec-strip: Implement arch-based filtering

This adds a new script - dh-exec-strip-arch-filter - that will strip
every line from the source that does not match the filters specified on
the line (lines without filters are left intact). Supports wildcards and
negation too.

Closes: Debian#757233
Requested-by: Andreas Henriksson <andreas@fatal.se>
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
t/test_strip.bats: Add another test, to be sure.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>