Support shell tracing inside functions even with ksh.

Support shell tracing inside functions even with ksh.

* libltdl/config/getopt.m4sh: Set $opt_debug to be either `:'
or `set -x' depending on whether --debug was parsed to match
usage in libtoolize.m4sh and ltmain.m4sh.
* clcommit.m4sh, libltdl/config/announce-gen.sh: Instead of
`$opt_debug && ...', use `test "$opt_debug" != ":" && ...'.
* clcommit.m4sh, libltdl/config/announce-gen.m4sh,
libltdl/config/getopt.m4sh, libltdl/connfig/mailnotify.m4sh:
Execute at the start of functions to cater to ksh, which
resets `-x' inside shell functions.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>