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.

- 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