I think I got it working now. Apparently the actual problem was the redirection to /dev/null in compile-sexp-to-c at compile-load.scm. Changing that to something else fixed it. There is also another /dev/null redirection in the lib.scm which might too cause problems.
Also when trying to compile the BH with --enable-single-host'ed Gambit I ran out of memory, is that to be expected?
How much memory are we speaking about?
It's 2 gt Windows 7/32 netbook with GCC 4.7.0.