zig.h: do not assume __GNUC__ is not clang (#2)

I missed this edit in 176940b5045ff0c9b20f9951dca34b2a1bb7edc0 .
db7b36f3fcMichael Dusan committed on 1/6/2023, 6:32:13 AM· committed by Andrew Kelleyparenta01d2ab
1 file changedLine totals unavailable