gcl27 fails to cross build from source for two main reasons. One reason
is that debian/rules forces a bare C compiler onto configure that would
otherwise choose a cross compiler. This is due to the MCC=gcc
assignment. Deferring the choice to dpkg's buildtools.mk is the usual
way to choose a compiler.

The other reason is use of AC_RUN_IFELSE. The configure.ac uses it in
lots of places and each of those makes cross compilation fail as host
code cannot be run. A significant chunk of those checks do not actually
need to run code. For instance, sizeof can be determined via compilation
bisection as is implemented in AC_CHECK_SIZEOF. The attached patch
converts a significant chunk of those checks and ideally it would be
forwarded upstream as it benefits other distributions such as Yocto. For
the remaining checks, AC_CACHE_CHECK probably is the way to go.

The attached patch significantly improves the situation without making
gcl27 cross buildable yet. Please close the bug report anyway when
addressing significant aspects of what is being reported here.

Helmut