looping m4 macro
the changed m4 macro in d598d8af :
AC_DEFUN([AM_PATH_XML2],[
AC_MSG_WARN([AM_PATH_XML2 is deprecated, use PKG_CHECK_MODULES instead])
...
loops forever (until m4 runs out of memory), seemingly because AM_PATH_XML2
is defined as a function, so it calls itself.
it should use m4_warn instead:
AC_DEFUN([AM_PATH_XML2],[
m4_warn([obsolete], [AM_PATH_XML2 is deprecated....])