based on patch by nik

note that object files using sigset_t (or struct sigaction) need to be
recompiled to work correctly after this fix.

thanks to Peter Mazinger (psm) for pointing many of these issues out
and submitting a patch on which this commit is loosely based

- hide all the legacy xxxxxx32 name cruft in syscall.h so the actual
source files can be clean and uniform across all archs.

- cleanup llseek/lseek and mmap2/mmap handling for 32/64 bit systems

- alternate implementation for nice if the target lacks nice syscall