[Issue 23411] ImportC: undefined identifier __builtin_nanf

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23411

--- Comment #1 from dave287091 at gmail.com ---
Note that adding:

    alias __builtin_nan = imported!"core.stdc.math".nan;
    alias __builtin_nanf = imported!"core.stdc.math".nanf;
    alias __builtin_nanl = imported!"core.stdc.math".nanl;

to __builtins.di does *not* solve the issue as then it cannot be used as a
static initializer:

Error: `nanf` cannot be interpreted at compile time, because it has no
available source code.

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