bootstrap, autoreconf: intransparent error reporting

[Bruno Haible]

Hi,

Here's a case where the errors from bootstrap and autoreconf don't help much.

How to reproduce:
- Use an automake 1.15 installation from source (not the one your distro
  has put in /usr).
- $ git clone https://github.com/rrthomas/enchant.git
  $ cd enchant
  $ cp /somewhere/pkg.m4 m4/pkg.m4
  $ ./autogen.sh
  [works fine]
  $ cd ..
- $ rm -rf enchant
- $ git clone https://github.com/rrthomas/enchant.git
  $ cd enchant
  $ ./autogen.sh
  ...
  bootstrap: running: autoreconf --symlink --install
  configure.ac:8: error: possibly undefined macro: dnl
        If this token and others are legitimate, please use m4_pattern_allow.
        See the Autoconf documentation.
  configure.ac:143: error: possibly undefined macro: AC_CHECK_HEADERS
  configure.ac:175: error: possibly undefined macro: AC_LANG_PUSH
  configure.ac:199: error: possibly undefined macro: AC_MSG_WARN
  configure.ac:203: error: possibly undefined macro: AC_LANG_POP
  configure.ac:214: error: possibly undefined macro: m4_default
  configure.ac:235: error: possibly undefined macro: AC_MSG_FAILURE
  autoreconf: autoconf failed with exit status: 1

Really, the undefined macro is PKG_CHECK_MODULES, not any of
AC_CHECK_HEADERS, AC_LANG_PUSH, AC_MSG_WARN, AC_LANG_POP, m4_default,
AC_MSG_FAILURE.

Bruno