For PR351:

* Ensure #includes are wrapped with appropriate HAVE_ guards
* Account for variations in time.h and sys/time.h inclusion.
* Add macros for getting wait(2) exit status correctly (per autoconf sugg.)
* Implement ThrowErrno in terms of strerror_r, strerror or none based on
  what is available on the platform.

llvm-svn: 19161