[Issue 23344] std.stdio: error: undefined identifier fputc_unlocked

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23344

--- Comment #2 from Iain Buclaw <ibuclaw at gdcproject.org> ---
Patch posted to fix immediate build error, real fix would be to add the missing
macros to druntime, then we can re-enable GCC_IO again.

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