this was originally written for an early draft of the library where
non-standard functions would reside in a static library separate from
the shared libc.so, which would implement a pure standard. the idea
was not to depend on an implementation-dependent __syscall_ret
function in the main libc. but it turned out to be better to put
everything in a single library for both static and dynamic linking
uses, and thus the (incomplete) remnants of this feature were just
enlarging the source and binary.

to i386.

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