Portability of preprocessor directives

[Paul D. Smith]

What is the word on portability of preprocessor directives?

I'm in particular thinking of things like "#if defined()",
"#elif !defined()", the && and || operators, etc.

How universal are these directives?  I'm talking here about GNU make,
which is part of the bootstrap toolset and so I'm still interested
(to some degree) in pre-ANSI compilers, etc.


Thanks...

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