The following macros check for certain operating systems that need special treatment for some programs, due to exceptional oddities in their header files or libraries. These macros are warts; they will be replaced by a more systematic approach, based on the functions they make available or the environments they provide.
This macro is obsolescent, as interactive Unix is obsolete, and Sun dropped support for it on 2006-07-23. New programs need not use this macro.
If possible, enable extensions to Posix on hosts that normally disable the extensions, typically due to standards-conformance namespace issues. This may involve defining
_POSIX_PTHREAD_SEMANTICS, which are macros used by Solaris. It also defines
_TANDEM_SOURCEfor the HP NonStop platform. This macro also has the combined effects of