Victor Costan cbb83a1d64 Migrate feature detection macro checks from #ifdef to #if. ...

The #if predicate evaluates to false if the macro is undefined, or
defined to 0. #ifdef (and its synonym #if defined) evaluates to false
only if the macro is undefined.

The new setup allows differentiating between setting a macro to 0 (to
express that the capability definitely does not exist / should not be
used) and leaving a macro undefined (to express not knowing whether a
capability exists / not caring if a capability is used).

PiperOrigin-RevId: 391094241

2021-08-16 18:26:33 +00:00

1.9 KiB

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