- update to 8.1.028
- 5.x got the header fix too, don't install replacement headers there 
- allow to override GXX_ROOT 
Note: you may see "as: Illegal seek" while compiling with icc (a simple test
didn't revealed the same message with icpc). I don't know the reason for it,
but the resulting executable seems to work, so I commit the update.
Thanks to: marius 
Requested by: mi