POSIX compatibility code
------------------------

This code exists to work around some common POSIX compatibility issues.

POSIX specifies that if the first line of a Makefile is ".POSIX:" then the
Makefile should be processed according to POSIX rules, including with CC=c99.
Further, c99 is required to understand the -lrt and -lxnet options (and ignore
them if the routines they specify linkage for are already in the standard C
library).  Unfortunately some systems fail or one or both of these accounts.