zig.h: Define zig_gnuc for both GCC and Clang and stop using __GNUC__.
There's only one spot in the header where we want to handle GCC but not Clang,
so just add an extra check there.
d19e1919daAlex Rønne Petersen committed on 12/3/2024, 10:57:20 AMparentdd1d9cc