gnu: automake: Adjust test suite to lack of /bin/sh.

* gnu/packages/autotools.scm (autoconf-wrapper): New variable.
  (automake): Use AUTOCONF-WRAPPER instead of AUTOCONF.
  Add `automake-skip-amhello-tests.patch' as an input.
  Add #:patches and #:phases arguments.
* gnu/packages/patches/automake-skip-amhello-tests.patch: New file.
* Makefile.am (dist_patch_DATA): Add it.