Portability updates for the HPE NonStop platform.

* rb/hpe:
  compat/regex/regcomp.c: define intptr_t and uintptr_t on NonStop
  git-compat-util.h: add FLOSS headers for HPE NonStop
  config.mak.uname: support for modern HPE NonStop config.
  transport-helper: drop read/write errno checks
  transport-helper: use xread instead of read