section of configure.in:
------------------------------------------
tslib_libs=""
AC_CHECK_HEADER(tslib.h,
  [
    tslib_libs="-ltslib"
    AC_DEFINE(HAVE_TSLIB, 1, [Build Ecore_X Module])
  ],[
    AC_MSG_RESULT("No tslib header found. No tslib support being built")
  ]
)
AC_SUBST(tslib_libs)
------------------------------------------

Bails with: error: possibly undefined macro: AC_DEFINE