algol68g fails to cross build from source, because it uses a number of
AC_RUN_IFELSE tests. That macro does not work for cross compilation as
running is what does not work. However, many of them simply check for
sizes of types (where AC_CHECK_SIZEOF can be used). It turns out that
sufficiently many can be replaced that cross building algol68g becomes
feasible. I'm attaching a patch for your convenience.

Helmut