For AArch64, the ring crate depends on the presence of this header and a definition
of getauxval.

The pre-index operator ('!') was missing at the end of the stp
instruction.

As a result, the stack pointer wasn't updated after the
store of the 64-bit pair and the stored values were basically lost when
follow on code used the stack for later store ops.

iscntrl: Didn't handle the EOF macro correctly
isgraph: Didn't handle '~' (tilde) correctly
ispunct: Several issues

Implement ttyname by adding fpath function to Sys. Remove realpath function and use fpath internally