Fixup arch features
Fixup arch features

1) We have enough registers to handle syscall6
2) UCLIBC_NO_UNDERSCORES has been replaced by option SYMBOL_PREFIX in Rules.mak

skristiansson/uClibc-or1k,skristiansson/uClibc-or1k,skristiansson/uClibc-or1k,skristiansson/uClibc-or1k