Could you be more specific instead of just saying some vague statements without giving any information? What problems have you encountered on *BSD systems?
OK, off the top of my head (not all apply to all forks):
- The math library (libm) is incomplete.
- The 'nm' command has non-standard syntax.
- The 'od' command has non-standard syntax.
- System headers require -D_BSD_SOURCE or similar.
- System headers disobey standards in other ways.
- Not using -fPIC on OpenBSD gives unusable executables.
System headers should only require BSD_SOURCE if you've asked for strict ansi mode, just like gnu headers require GNU_SOURCE.
The glibc headers work perfectly in strict C99 mode. The BSD headers do not.