tests: avoid spurious failure of libtool and gettext tests

tests: avoid spurious failure of libtool and gettext tests

On Solaris 10 (and presumably earlier), /bin/sh trips up on
here-documents that contains a command substitution *and* are
fed to a shell function:

  # All as expected.
  $ cat <<END
  `pwd`
  END
  /home/stefano
  $ echo status = $?
  status = 0

  # An apparently innocuous function ...
  $ kitty () { cat; }
  # ... but hilarity ensues!
  $ kitty <<END
  `pwd`
  END
  /tmp/sh137723: cannot open
  $ echo status = $?
  status = 1

We need to work around this misbehaviour in a couple of our
tests (whose failures where causing cascading failures in a
lot of other tests).

* tests/gettext-macros.test: Avoid the use of command substitution
in a here-document passed to the `indent' function, by using the
`echo' builtin instead.
* tests/libtool-macros.test: Likewise.

See also:
<http://lists.gnu.org/archive/html/bug-autoconf/2011-12/msg00001.html>