linux: Add prlimit64 C implementation

The LFS prlimit64 requires a arch-specific implementation in
syscalls.list.  Instead add a generic one that handles the
required symbol alias for __RLIM_T_MATCHES_RLIM64_T.

HPPA is the only outlier which requires a different default
symbol.

Checked on x86_64-linux-gnu and with build for the affected ABIs.