Fix glibc specific conditional for Mac OS/X

[paulidale]

MacOS seems to define GLIBC but not __GLIBC_PREREQ.

The issue was reported against this commit. It follows on from the changes in #5231

[paulidale]

An alternative solution would be to conditionally define __GLIBC_PREREQ:

#ifndef __GLIBC_PREREQ
#define __GLIBC_PREREQ(a, b) (0)
#endif

somewhere.

[paulidale]

@lodenos this might help.

[paulidale]

Thanks @richsalz
Merged

[dot-asm]

It's like producing least readable code was the purpose. I mean _POSIX_C_SOURCE is about same thing, so why is there another thing in between? Basically both _POSIX_C_SOURCE should be in parentheses to denote it's about same thing. As for _POSIX_TIMERS and MacOS X context. It's defined as -1, while Linux(*) man page says it's positive.

(*) It's not clear if we can hold Linux man pages as official standard, one should check POSIX specs.

[dot-asm]

BTW, referred comment asks "work?", this conversation says "might help". You know what? It doesn't work. In fact it doesn't work on any system [that attempts to compile this] but Linux.

[paulidale]

Which systems doesn't this work for?
Our CI builds for Windows & Solaris built okay. AIXand HP/UX didn't for a different reason.

That conditional is getting complex. Grouping the _POSIX_C_SOURCE checks makes sense and was missed on the previous commit. Would the alternative of defining __GLIBC_PREREQ if it isn't already defined help? I could also add a comment about what it is trying to achieve.

[dot-asm]

Which systems doesn't this work for?

Once again, any that tries to compile it and is not Linux, such as MacOS X, *BSD, OSF, IRIX... VMS ought to fail too...

[paulidale]

In what way isn't this conditional working? I'm confused.

[dot-asm]

Just remove __sun condition and see for yourself on Solaris.

[paulidale]

Thanks, got it now. PR coming.

[mouse07410]

Which systems doesn't this work for?

it does not work for MacOS El Capitan, Sierra, and High Sierra. See #5290.