I'm digging on old compiler versions for bootstrapping purposes and I realized that gcc 4.7 and 4.8 packages don't compile on x64.
We have been able to reproduce the failure of gcc 4.7 but we didn't test the 4.8 error that far.
In gcc-4.7 the error is the following:
./md-unwind-support.h:60:47: error: dereferencing pointer to incomplete type
I guess there's something missing there but I'm out of ideas to dig on this further.